MDL-52204 grunt: update to grunt-contrib-jshint v0.11.3

This version of grunt-contrib-jshint itself uses a better fixed
requirement on "~2.8.0" rather than "^2.8.0" which was giving variable
results with some people updating to 2.9-rc1.

See also https://github.com/gruntjs/grunt-contrib-jshint/pull/219

package.json

@@ -4,7 +4,7 @@
     "description": "Moodle",
     "devDependencies": {
         "grunt": "0.4.5",
-        "grunt-contrib-jshint": "0.11.2",
+        "grunt-contrib-jshint": "0.11.3",
         "grunt-contrib-less": "1.1.0",
         "grunt-contrib-uglify": "0.9.1",
         "shifter": "0.5.0",