clang/release notes: s/Subversion/git/

Author: sylvestre

clang/docs/ReleaseNotes.rst

@@ -581,7 +581,7 @@ Additional Information
 
 A wide variety of additional information is available on the `Clang web
 page <https://clang.llvm.org/>`_. The web page contains versions of the
-API documentation which are up-to-date with the Subversion version of
+API documentation which are up-to-date with the Git version of
 the source code. You can access versions of these documents specific to
 this release by going into the "``clang/docs/``" directory in the Clang
 tree.