cli_spec.rb: prefer BUNDLE_RUBY
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59821 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
cli_spec.rb: prefer BUNDLE_RUBY
hack. on macOS 10.11 or later, some system commands, e.g.
/bin/sh and /usr/bin/env, clear DYLD_LIBRARY_PATH environment
variable which is necessary to run not-yet installed command.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59821 b2dd03c8-39d4-4d8f-98ff-823fe69b080e