Merge pull request #690 from borgified/fix_url

fix broken url

free-programming-books.md

@@ -1616,4 +1616,4 @@ See also [LaTeX](#latex)
 ###xBase (dBase / Clipper / Harbour)
 * [Application Development with Harbour](http://en.wikibooks.org/wiki/Application_Development_with_Harbour)
 * [CA-Clipper 5.2 Norton Guide](http://www.ousob.com/ng/clguide/)
-* [Clipper Tutorial: a Guide to Open Source Clipper(s)](http://en.wikibooks.org/wiki/Clipper_Tutorial:_a_Guide_to_Open_Source_Clipper(s%29)
+* [Clipper Tutorial: a Guide to Open Source Clipper(s)](http://en.wikibooks.org/wiki/Clipper_Tutorial:_a_Guide_to_Open_Source_Clipper(s))