ZipLoader: Remove default from_path value

We are now able to calculate it on our own so it has become bothering
to have it by default

gadget/gadget_zip_loader.js

@@ -94,7 +94,7 @@
       if ( params.hasOwnProperty("from_path") ) {
         gadget.props.element.querySelector("form.crib-load-from-zip-url .load-from-zip-path").value = params.from_path;
       } else {
-        gadget.props.element.querySelector("form.crib-load-from-zip-url .load-from-zip-path").value = "cribjs-editor-master/";
+        gadget.props.element.querySelector("form.crib-load-from-zip-url .load-from-zip-path").value = "";
       }
       if ( params.hasOwnProperty("to_path") ) {
         gadget.props.element.querySelector("form.crib-load-from-zip-url .load-zip-to-path").value = params.to_path;