Don't run Sauce Labs tests on pull requests

Due to security restrictions within Travis CI, we cannot use secure
environment variables in pull requests.  This means that the tests
cannot be run in the Sauce Labs environment.

http://docs.travis-ci.com/user/pull-requests/#Security-Restrictions-when-testing-Pull-Requests

Gruntfile.js

@@ -317,10 +317,20 @@ module.exports = function (grunt) {
   grunt.registerTask('minify', ['uglify', 'sass:dist']);
   grunt.registerTask('test', ['connect:tests', 'qunit', 'jshint']);
 
-  grunt.registerTask('ci', [
-    'compile', 'connect:tests',
-    'saucelabs-qunit', 'qunit', 'jshint'
-  ]);
+  var ciTasks = [];
+
+  ciTasks.push('compile')
+  ciTasks.push('connect:tests');
+
+  // Can't run Sauce Labs tests in pull requests
+  if (process.env.TRAVIS_PULL_REQUEST == null) {
+    ciTasks.push('saucelabs-qunit');
+  }
+
+  ciTasks.push('qunit');
+  ciTasks.push('jshint');
+
+  grunt.registerTask('ci', ciTasks);
 
   grunt.registerTask('docs', ['symlink:docs', 'jekyll:serve']);