Upgrade grunt-preprocess to be compatible with Grunt 1.x

This upgrades grunt-preprocess to v5.1.0, which is both the latest version and the first version that declares itself compatible with Grunt 1.x. Previous versions *appeared* to work fine, but caused peer dependency warnings, which this fixes. It also resolves a few security vulnerabilities along the way.

package.json

@@ -48,7 +48,7 @@
     "grunt-coveralls": "^1.0.0",
     "grunt-jasmine-node": "~0.2.1",
     "grunt-open": "~0.2.3",
-    "grunt-preprocess": "^4.0.0",
+    "grunt-preprocess": "^5.1.0",
     "grunt-saucelabs": "^8.2.0",
     "grunt-template-jasmine-istanbul": "~0.4.0",
     "qunitjs": "1.14.0",