Cleanup overArg description. [ci skip]

lodash.js

@@ -1129,7 +1129,7 @@
   }
 
   /**
-   * Creates a function that invokes `func` with its first argument transformed.
+   * Creates a unary function that invokes `func` with its argument transformed.
    *
    * @private
    * @param {Function} func The function to wrap.