Clean up Not Found error message

Author: cletusw

index.js

@@ -11,8 +11,8 @@ var rules = requireUp('eslint-local-rules', __dirname);
 if (!rules) {
   throw new Error(
     'eslint-plugin-local-rules: ' +
-    'Cannot find "eslint-local-rules.{' + exts.join(',') + "}" +
-    '(looking up from "' + __dirname + '").'
+    'Cannot find "eslint-local-rules{' + ['.js'].concat(exts.filter(Boolean)) + "} " +
+    'or eslint-local-rules/index.js (checked all ancestors of "' + __dirname + '").'
   );
 }