Fix heading of README.

[Fix GH-1586] Patch by @jbampton git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58393 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
2017-04-18 11:55:44 +00:00 · 2017-04-18 11:55:44 +00:00 · 97a114de44
--- a/README.md
+++ b/README.md
@ -157,7 +157,7 @@ Bug reports should be filed at https://bugs.ruby-lang.org. Read [HowToReport] fo

 [HowToReport]: https://bugs.ruby-lang.org/projects/ruby/wiki/HowToReport

-##Contributing
+## Contributing

 See the file [CONTRIBUTING.md](CONTRIBUTING.md)