runnable.js: fix async skip()

lib/runnable.js

@@ -343,11 +343,7 @@ Runnable.prototype.run = function(fn) {
 
     // allows skip() to be used in an explicit async context
     this.skip = function asyncSkip() {
-      done(new Pending('async skip call'));
-      // halt execution.  the Runnable will be marked pending
-      // by the previous call, and the uncaught handler will ignore
-      // the failure.
-      throw new Pending('async skip; aborting execution');
+      return done(new Pending('async skip call'));
     };
 
     if (this.allowUncaught) {