Allow for locally chosen rubies

By ignoring .versions.conf, we can allow users pick their own versions
of ruby without having to jump through a bunch of hoops on keeping
.ruby-version straight between local and remote branches.

Author: Tod Beardsley

.gitignore

@@ -7,6 +7,10 @@ Gemfile.local.lock
 .sublime-project
 # RVM control file, keep this to avoid backdooring Metasploit
 .rvmrc
+# Allow for a local choice of (unsupported / semi-supported) ruby versions
+# See PR #4136 for usage, but example usage:
+#   rvm --create --versions-conf use # 2.1.4@metasploit-framework
+.versions.conf
 # YARD cache directory
 .yardoc
 # Mac OS X files