Remove unused Grunt version task; flesh out docs on how to do a rel…

…ease a bit (#510)

* Tweak CONTRIBUTING.md to use the 'release' task, which includes a license in diff.js and diff.min.js (omitted in v5.2.0 by mistake)

* Delete pointless/unused 'version' Grunt task

There's no reference to this in any docs and as far as I can tell there's no reason I'd ever want to run it.

* Flesh out docs on how to do a release a bit more

* Flesh out reminder even more, for the sake of future idiots (e.g. me)

CONTRIBUTING.md

@@ -26,13 +26,15 @@ If you notice any problems, please report them to the GitHub issue tracker at
 
 ## Releasing
 
-A full release may be completed with the following:
+A full release may be completed by first updating the `"version"` property in package.json, then running the following:
 
 ```
 yarn clean
-yarn grunt
-yarn grunt uglify
+yarn grunt release
 yarn publish
 ```
 
-After releasing, remember to update `diff.js` on the `gh-pages` branch to the latest built version from the `dist/` folder.
+After releasing, remember to:
+* commit the `package.json` change and push it to GitHub
+* create a new version tag on GitHub
+* update `diff.js` on the `gh-pages` branch to the latest built version from the `dist/` folder.

Gruntfile.js

@@ -139,8 +139,6 @@ module.exports = function(grunt) {
   grunt.loadNpmTasks('grunt-mocha-istanbul');
   grunt.loadNpmTasks('grunt-exec');
 
-  grunt.task.loadTasks('tasks');
-
   grunt.registerTask('dev', ['clean', 'watch']);
   grunt.registerTask('default', ['clean', 'build', 'cover']);
 };