Fix commit_bump

Author: nobu

rakelib/version.rake

@@ -12,7 +12,7 @@ class << (helper = Bundler::GemHelper.instance)
   end
 
   def commit_bump
-    sh(%W[git -C #{__dir__} commit -m bump\ up\ to\ #{gemspec.version}
+    sh(%W[git commit -m bump\ up\ to\ #{gemspec.version}
           #{gemspec.loaded_from}])
   end