Bump version to v7.1.0 (#1562)

Bump to v7.1.0 to release the recent fixes and improvements.

Comparison since the last tag:

https://github.com/ruby/rdoc/compare/v7.0.3...master?expand=1

Author: vinistock

lib/rdoc/version.rb

@@ -5,6 +5,6 @@ module RDoc
   ##
   # RDoc version you are using
 
-  VERSION = '7.0.3'
+  VERSION = '7.1.0'
 
 end