Install ruby when custom stacks are used

Author: dsabeti

bin/run

@@ -93,7 +93,7 @@ function main() {
   local phase
   phase="$(basename "${0}")"
 
-  if [[ "${CF_STACK:-}" == "cflinuxfs4" ]]; then
+  if [[ "${CF_STACK:-}" != "cflinuxfs3" ]]; then
     if ! which ruby > /dev/null; then
       mkdir -p "${RUBY_DIR}"