Please check if the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

• [*] Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior? (You can also link to an open issue here)

lib/karma-webpack.js has the following line:

var _toConsumableArray2 = require('babel-runtime/helpers/toConsumableArray');

When using pnpm, the babel-runtime is marked as a devDependency and therefore not included in the node_modules. Hence you get the following error:

27 02 2018 10:54:19.765:ERROR [config]: Invalid config file!
  Error: Cannot find module 'babel-runtime/helpers/toConsumableArray'
    at Function.Module._resolveFilename (module.js:469:15)
    at Function.Module._load (module.js:417:25)
    at Module.require (module.js:497:17)
    at require (internal/module.js:20:19)
    at Object.<anonymous> (D:\GitRepos\sp-client2\common\temp\node_modules\.onedrive.pkgs.visualstudio.com\karma-webpack\2.0.12\webpack@3.6.0\node_modules\karma-webpack\lib\karma-webpack.js:3:27)

What is the new behavior?

The babel-runtime is installed as a runtime dependency.

Does this PR introduce a breaking change?

• Yes
• [*] No

If this PR contains a breaking change, please describe the following...

• Impact:
• Migration path for existing applications:
• Github Issue(s) this is regarding:

Other information: