doc: workaround to npm shrinkwrap development dependencies bug

There are some npm versions that for some strange reason will attempt to
put *every* single development dependency in the `npm-shinkwrap.json`
file when editing the dependencies list.

This commit describes a workaround I've found to ensure only production
dependencies are added to the file.

I also renamed our `npm run shrinkwrap` script to `npm run
clean-shrinkwrap` since in some recent versions of npm, running `npm
shrinkwrap` will trigger our custom script instead of the original
implementation.

Signed-off-by: Juan Cruz Viotti <jviotti@openmailbox.org>

docs/CONTRIBUTING.md

@@ -44,9 +44,20 @@ Use the following steps to ensure everything goes flawlessly:
 - Install the new version of the dependency. For example: `npm install --save
   <package>@<version>`. This will update the `npm-shrinkwrap.json` file.
 
-- Run `npm run shrinkwrap`. This is a small script that ensures that operating
-  system specific dependencies that could get included in the previous step are
-  removed from `npm-shrinkwrap.json`.
+- Run `npm run clean-shrinkwrap`. This is a small script that ensures that
+  operating system specific dependencies that could get included in the
+  previous step are removed from `npm-shrinkwrap.json`.
+
+Some npm versions seem to contain an issue were all development dependencies
+will be included in `npm-shrinkwrap.json` when attempting to modify it (e.g: by
+`npm install`, `npm uninstall`, etc). A bulletproof way to ensure only the
+necessary dependencies get added is to run the following commands:
+
+```sh
+make electron-develop
+npm prune --production
+npm shrinkwrap
+```
 
 - Commit *both* `package.json` and `npm-shrinkwrap.json`.
 

package.json

@@ -18,7 +18,7 @@
     "lint": "npm run jslint && npm run scsslint",
     "changelog": "versionist",
     "start": "electron lib/start.js",
-    "shrinkwrap": "node ./scripts/shrinkwrap.js"
+    "clean-shrinkwrap": "node ./scripts/clean-shrinkwrap.js"
   },
   "author": "Juan Cruz Viotti <juan@resin.io>",
   "license": "Apache-2.0",