antlr download link in readme file is incorrect

The antlr download link provided by the readme file is http://www.antlr.org/download/antlr-3.5-complete.jar, but the link has broken.

 the new link is http://www.antlr3.org/download/antlr-3.5-complete.jar
Merge pull request #56 from hellojinjie/patch-1

antlr download link in readme file is incorrect