replace trailing whitespace with blackslash in README.md

As an alternative to the markdown trailing whitespace as a line
break, we use a trailing blackslash as a markdown line break.

2014/endoh1/README.md

@@ -2,7 +2,7 @@
 
 Yusuke Endoh<br>
 <mame@ruby-lang.org><br>
-<https://github.com/mame/>  
+<https://github.com/mame/>\
 Mastodon: [@mame@ruby.social](https://ruby.social/@mame)
 
 ## To build: