[clang-tidy] update links to Google Code Style in docs

Summary: Because of the recent Google Code shutdown links to the Google Code Style up there are no longer relevant.

Reviewers: alexfh, hokein

Subscribers: cfe-commits

Patch by Kirill Bobyrev!

Differential Revision: http://reviews.llvm.org/D17602

llvm-svn: 261868
diff --git a/clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.h b/clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.h
index aa98ad8..ea7e34c 100644
--- a/clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.h
+++ b/clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.h
@@ -19,7 +19,7 @@
 
 /// Finds usages of C-style casts.
 ///
-/// http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Casting#Casting
+/// https://google.github.io/styleguide/cppguide.html#Casting
 ///
 /// Corresponding cpplint.py check name: 'readability/casting'.
 ///