安装Bower时为什么会出现此错误（npm）

Question

我想安装Polymer 2，为此我需要安装Bower。

当我这样做时

npm install -g bower

我得到了

npm ERR! path C:\Users\xxx\AppData\Roaming\npm\node_modules\bower
npm ERR! code ENOENT
npm ERR! errno -4058
npm ERR! syscall rename
npm ERR! enoent ENOENT: no such file or directory, rename 'C:\Users\xxx\AppData\Roaming\npm\node_modules\bower' -> 'C:\Users\xxx\AppData\Roaming\npm\node_modules\.bower.DELETE'
npm ERR! enoent This is related to npm not being able to find a file.
npm ERR! enoent

npm ERR! A complete log of this run can be found in:
npm ERR!     C:\Users\xxx\AppData\Roaming\npm-cache\_logs\2018-03-19T23_03_27_559Z-debug.log

日志文件是：

    0 info it worked if it ends with ok
    1 verbose cli [ 'C:\\Program Files\\nodejs\\node.exe',
    1 verbose cli   'C:\\Program Files\\nodejs\\node_modules\\npm\\bin\\npm-cli.js',
    1 verbose cli   'install',
    1 verbose cli   '-g',
    1 verbose cli   'bower' ]
    2 info using npm@5.6.0
    3 info using node@v8.10.0
    4 verbose npm-session 678db3b2d10cf1b3
    5 silly install loadCurrentTree
    6 silly install readGlobalPackageData
    7 http fetch GET 200 https://registry.npmjs.org/bower 375ms
    8 silly pacote tag manifest for bower@latest fetched in 437ms
    9 warn deprecated bower@1.8.2: ...psst! Your project can stop working at any moment because its dependencies can change. Prevent this by migrating to Yarn: https://bower.io/blog/2017/how-to-migrate-away-from-bower/
    10 silly install loadIdealTree
    11 silly install cloneCurrentTreeToIdealTree
    12 silly install loadShrinkwrap
    13 silly install loadAllDepsIntoIdealTree
    14 silly resolveWithNewModule bower@1.8.2 checking installable status
    15 silly currentTree npm
    16 silly idealTree npm
    16 silly idealTree `-- bower@1.8.2
    17 silly install generateActionsToTake
    18 silly diffTrees action count 1
    19 silly diffTrees add bower@1.8.2
    20 silly decomposeActions action count 8
    21 silly decomposeActions fetch bower@1.8.2
    22 silly decomposeActions extract bower@1.8.2
    23 silly decomposeActions preinstall bower@1.8.2
    24 silly decomposeActions build bower@1.8.2
    25 silly decomposeActions install bower@1.8.2
    26 silly decomposeActions postinstall bower@1.8.2
    27 silly decomposeActions finalize bower@1.8.2
    28 silly decomposeActions refresh-package-json bower@1.8.2
    29 silly install executeActions
    30 silly doSerial global-install 8
    31 verbose correctMkdir C:\Users\xxx\AppData\Roaming\npm-cache\_locks correctMkdir not in flight; initializing
    32 verbose makeDirectory C:\Users\xxx\AppData\Roaming\npm-cache\_locks creation not in flight; initializing
    33 verbose makeCacheDir UID & GID are irrelevant on win32
    34 verbose lock using C:\Users\xxx\AppData\Roaming\npm-cache\_locks\staging-b87bd1c8617be94e.lock for C:\Users\xxx\AppData\Roaming\npm\node_modules\.staging
    35 silly doParallel extract 8
    36 silly extract bower@1.8.2
    37 silly pacote trying bower@https://registry.npmjs.org/bower/-/bower-1.8.2.tgz by hash: sha1-rfU1KcjUrwLvJPuNU0HBQZ0z4vc=
    38 silly pacote data for sha1-rfU1KcjUrwLvJPuNU0HBQZ0z4vc= not present. Using manifest.
    39 http fetch GET 200 https://registry.npmjs.org/bower/-/bower-1.8.2.tgz 3375ms
    40 silly pacote bower@https://registry.npmjs.org/bower/-/bower-1.8.2.tgz extracted in 3375ms
    41 silly doReverseSerial unbuild 8
    42 silly doSerial remove 8
    43 silly doSerial move 8
    44 silly doSerial finalize 8
    45 silly finalize C:\Users\xxx\AppData\Roaming\npm\node_modules\bower
    46 verbose unlock done using C:\Users\xxx\AppData\Roaming\npm-cache\_locks\staging-b87bd1c8617be94e.lock for C:\Users\xxx\AppData\Roaming\npm\node_modules\.staging
    47 verbose stack Error: ENOENT: no such file or directory, rename 'C:\Users\xxx\AppData\Roaming\npm\node_modules\bower' -> 'C:\Users\xxx\AppData\Roaming\npm\node_modules\.bower.DELETE'
    48 verbose cwd C:\BookaPolymer
    49 verbose Windows_NT 10.0.16299
    50 verbose argv "C:\\Program Files\\nodejs\\node.exe" "C:\\Program Files\\nodejs\\node_modules\\npm\\bin\\npm-cli.js" "install" "-g" "bower"
    51 verbose node v8.10.0
    52 verbose npm  v5.6.0
    53 error path C:\Users\xxx\AppData\Roaming\npm\node_modules\bower
    54 error code ENOENT
    55 error errno -4058
    56 error syscall rename
    57 error enoent ENOENT: no such file or directory, rename 'C:\Users\xxx\AppData\Roaming\npm\node_modules\bower' -> 'C:\Users\xxx\AppData\Roaming\npm\node_modules\.bower.DELETE'
    58 error enoent This is related to npm not being able to find a file.
    59 verbose exit [ -4058, true ]

为什么我会这样做？