Update releases.rb

Author: Cobra-Bitcoin

_plugins/releases.rb

@@ -34,7 +34,7 @@ def initialize(site, base, lang, srcdir, src, output_directory)
       end
 
       ## Output file is v<version>.md (converted later to HTML)
-      output_file = "v" + version + ".md"
+      output_file = "v" + version.to_s + ".md"
       @name = output_file
       self.process(output_file)