解决node-gyp报错：KeyError 2017

node-gyp因为不兼容Visual Studio 2017，所以报错：KeyError:2017，它的检测代码是node-gyp模块下一个名为
MSVersion.py文件，第434行代码：

def SelectVisualStudioVersion(version='auto', allow_fallback=True):
  """Select which version of Visual Studio projects to generate.

  Arguments:
    version: Hook to allow caller to force a particular version (vs auto).
  Returns:
    An object representing a visual studio project format version.
  """
  # In auto mode, check environment variable for override.
  if version == 'auto':
    version = os.environ.get('GYP_MSVS_VERSION', 'auto')
  version_map = {
    'auto': ('14.0', '12.0', '10.0', '9.0', '8.0', '11.0'),
    '2005': ('8.0',),
    '2005e': ('8.0',),
    '2008': ('9.0',),
    '2008e': ('9.0',),
    '2010': ('10.0',),
    '2010e': ('10.0',),
    '2012': ('11.0',),
    '2012e': ('11.0',),
    '2013': ('12.0',),
    '2013e': ('12.0',),
    '2015': ('14.0',),
  }
  override_path = os.environ.get('GYP_MSVS_OVERRIDE_PATH')
  if override_path:
    msvs_version = os.environ.get('GYP_MSVS_VERSION')
    if not msvs_version:
      raise ValueError('GYP_MSVS_OVERRIDE_PATH requires GYP_MSVS_VERSION to be '
                       'set to a particular version (e.g. 2010e).')
    return _CreateVersion(msvs_version, override_path, sdk_based=True)
  version = str(version)
  versions = _DetectVisualStudioVersions(version_map[version], 'e' in version)
  if not versions:
    if not allow_fallback:
      raise ValueError('Could not locate Visual Studio installation.')
    if version == 'auto':
      # Default to 2005 if we couldn't find anything
      return _CreateVersion('2005', None)
    else:
      return _CreateVersion(version, None)
  return versions[0]

从代码逻辑可以看出，它支持两个环境变量：GYP_MSVS_VERSION与GYP_MSVS_OVERRIDE_PATH。
我在执行npm install之前首先运行：

set GYP_MSVS_VERSION=2015
set GYP_MSVS_OVERRIDE_PATH=C:\Program Files (x86)\Microsoft Visual Studio 14.0

问题就解决了。
最后提示：请确认当前机器安装了Visual Studio 2015。我的机器同时安装了两个版本。