Tiny cosmetics in error message of pick()

lib/utils/objects.js

@@ -38,7 +38,7 @@ Objects.prototype.pick = function (category, last) {
     return this.get(category, last).name
   } catch (e) {
     logger.traceback()
-    throw logger.JSError('Error: pick(' + category + ') ' + category + ' is undefined.')
+    throw logger.JSError('Error: pick(\'' + category + '\') is undefined.')
   }
 }