Changed 'ruby' option to 'ruby-executable' to be more like 'executable' which

specifies python executable.

rubygems.py

@@ -30,7 +30,7 @@ class Recipe(object):
         self.gems = options['gems'].split()
         self.version = options.get('version')
         # Allow to define specific ruby executable. If not, take just 'ruby'
-        self.ruby_executable = options.get('ruby', 'ruby')
+        self.ruby_executable = options.get('ruby-executable', 'ruby')
 
     def run(self, cmd, environ=None):
         """Run the given ``cmd`` in a child process."""