Log the actual promise object instead of a useless name

- console.log has support for objects including introspection, use this
 - instead of logging useless names

app/views/common/_discourse_javascript.html.erb

@@ -20,7 +20,7 @@
           console.log(e.message);
           console.log(e.stack);
         } else {
-          console.log("Uncaught promise: " + e.toString());
+          console.log("Uncaught promise: ", e);
         }
       } else {
         console.log("A promise failed but was not caught.");