What's the best way to run a ruby executable from a specific rbenv version?

output

$ ruby -v
ruby 1.9.3p545 (2014-02-24 revision 45159) [x86_64-darwin13.1.0]

$ rbenv exec travis --version
rbenv: travis: command not found

The `travis' command exists in these Ruby versions:
  2.1.1

$ which travis
/Users/Larry/.bin/travis

$ travis --version
1.6.14

travis

#!/usr/bin/env bash

# Run travis installed in ruby 2.1.1
export RBENV_VERSION=2.1.1
exec rbenv exec travis $@