Remove custom caching and use Bundle for gems.

Gruntfile.js

@@ -301,7 +301,9 @@ module.exports = function (grunt) {
 
     jekyll: {
       options: {
-        config: '_config.yml'
+        bundleExec: true,
+        config: '_config.yml',
+        incremental: false
       },
       docs: {},
       github: {
@@ -501,7 +503,7 @@ module.exports = function (grunt) {
       if (err) {
         grunt.fail.warn(err);
       }
-      var dest = 'test-infra/npm-shrinkwrap.json';
+      var dest = 'grunt/npm-shrinkwrap.json';
       fs.renameSync('npm-shrinkwrap.json', dest);
       grunt.log.writeln('File ' + dest.cyan + ' updated.');
       done();