Enable the object-shorthand ESLint rule in src/shared

Please see http://eslint.org/docs/rules/object-shorthand.

For the most part, these changes are of the search-and-replace kind, and the previously enabled `no-undef` rule should complement the tests in helping ensure that no stupid errors crept into to the patch.

src/core/image.js

@@ -280,7 +280,7 @@ var PDFImage = (function PDFImageClosure() {
       }
     }
 
-    return {data: data, width: width, height: height};
+    return { data, width, height, };
   };
 
   PDFImage.prototype = {