feat(grunt): adds a release task check to ensure the branch is master

If you run the release grunt task while not in the master branch,
the repo will get trashed. After personally experiencing this,
I created this check to prevent this from happening in the future.

gruntfile.js

@@ -28,6 +28,15 @@ module.exports = function (grunt) {
     }
   }
 
+  /**
+   * Removes whitespace from a given string.
+   * @param  {String} string The string you wish to trim.
+   * @return {String}        The trimmed string.
+   */
+  function trim(string) {
+    return string.replace(/[\s]/g, '');
+  }
+
   // the workhorse of the grunt file
   grunt.initConfig({
     // inject specific header
@@ -76,12 +85,23 @@ module.exports = function (grunt) {
         command: 'git describe HEAD',
         options: {
           callback: function (err, stdout, stderr, next) {
-            var version = stdout.replace(/[\s]/g, '');
+            var version = trim(stdout);
             setVersion(version);
             next();
           }
         }
       },
+      isBranchMaster: {
+        command: 'git rev-parse --abbrev-ref HEAD',
+        options: {
+          callback: function (err, stdout, stderr, next) {
+            if (trim(stdout) !== 'master') {
+              throw new Error('You have not checked out the master branch.');
+            }
+            next();
+          }
+        }
+      },
       git_add: {
         command: 'git add -A',
         options: {
@@ -435,6 +455,7 @@ module.exports = function (grunt) {
   ]);
 
   grunt.registerTask('release', [
+    'shell:isBranchMaster',
     'build',
     'releasetest',
     'copy:recent_to_release',