Make compatible with latest JSHint.

grunt.js

@@ -12,6 +12,8 @@ var child_process = require("child_process");
 
 module.exports = function( grunt ) {
 
+	"use strict";
+
 	// readOptionalJSON
 	// by Ben Alman
 	// https://gist.github.com/2876125

src/ajax/xhr.js

@@ -150,7 +150,7 @@ if ( jQuery.support.ajax ) {
 									// on any attempt to access responseText (#11426)
 									try {
 										responses.text = xhr.responseText;
-									} catch( _ ) {
+									} catch( e ) {
 									}
 
 									// Firefox throws an exception when accessing