with_clean_env should clean BUNDLER_ variabls
with_clean_env should clean BUNDLER_ variabls

In version 1.13.0, bundler moved from BUNDLE_ to BUNDLER_ as the
prefix for their environment variables.

Signed-off-by: Steven Danna <9ce5770b3bb4b2a1d59be2d97e34379cd192299f@chef.io>

Altiscale/omnibus,Altiscale/omnibus,rapid7/omnibus,rapid7/omnibus,rapid7/omnibus,chef/omnibus,chef/omnibus,Altiscale/omnibus,chef/omnibus