Fix grunt build task useminPrepare and imagemin errors

On the grunt build task, grunt was issuing the following errors:
Running "useminPrepare:html" (useminPrepare) task
Warning: An error occurred while processing a template (Unexpected token )). Use --force to continue.

Running "imagemin:dist" (imagemin) task
Warning: An error occurred while processing a template (Unexpected token )). Used --force, continuing.

The bug was caused by additional '%' characters added to the closing template
stings on the imagemin task in the gruntfile.

Resolves: #632

app/templates/Gruntfile.js

@@ -298,9 +298,9 @@ module.exports = function (grunt) {
           dest: '<%%= config.dist %>/images'
         },{
           expand: true,
-          cwd: '<%%= config.app %%>',
+          cwd: '<%%= config.app %>',
           src: '*.{ico,png}',
-          dest: '<%%= config.dist %%>'
+          dest: '<%%= config.dist %>'
         }]
       }
     },