pass gemfile through the env var
pass gemfile through the env var

Use BUNDLE_GEMFILE environment variable instead of --gemfile option when
invoking `bundle install` in the `spec:install` rake task.
It helps to avoid weird `Specs already loaded (RuntimeError)` error in
this rake task.

jweslley/nested_form,myaidin/nested_form,alphagov/nested_form,partheey-vakilsearch/nested_form,ryanb/nested_form,fxposter/nested_form,cuongnguyen2503/nested_form,tomasdundacek/nested_form,Stellenticket/nested_form,partheey-vakilsearch/nested_form,dhunnapotha/nested_form,pinglamb/nested_form,ryanb/nested_form,Stellenticket/nested_form,pinglamb/nested_form,fxposter/nested_form,cuongnguyen2503/nested_form,jweslley/nested_form,dhunnapotha/nested_form,dhunnapotha/nested_form,myaidin/nested_form,jweslley/nested_form,alphagov/nested_form,partheey-vakilsearch/nested_form,pinglamb/nested_form,myaidin/nested_form,tomasdundacek/nested_form,Stellenticket/nested_form,cuongnguyen2503/nested_form