update link to point to github instead of googlecode

cpplint/README

@@ -1,5 +1,5 @@
 This is automated checker to make sure a C++ file follows Google's C++ style
-guide (http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml). As it
+guide (http://google.github.io/styleguide/cppguide.html). As it
 heavily relies on regular expressions, cpplint.py won't catch all violations of
 the style guide and will very occasionally report a false positive. There is a
 list of things we currently don't handle very well at the top of cpplint.py,