Enable npm's package-lock feature

The `package-lock.json` (1) file was disabled in the global `npmrc` (2)
file since it hasn't been used due to a various problems regarding merge
conflicts and unintended transitive dependency updates on each
`npm install`. These problems haven been fixed in later npm release
versions. This allows to use this feature again to ensure stable and
reproducible builds.

References:

  (1) https://docs.npmjs.com/files/package-lock.json
  (2) https://github.com/arcticicestudio/igloo/blob/develop/snowblocks/npm/npmrc

Closes GH-142

snowblocks/npm/npmrc

@@ -10,5 +10,5 @@ init-author-email=development@arcticicestudio
 init-author-url=http://arcticicestudio.com
 init-version=0.0.0
 init-license=MIT
-package-lock=false
+package-lock=true
 save-exact=true