disable simplecov on jruby

Doesn't seem to work at all on 9.1.2.0

Author: JonRowe

script/functions.sh

@@ -28,7 +28,7 @@ function run_specs_and_record_done {
 
   # rspec-core needs to run with a special script that loads simplecov first,
   # so that it can instrument rspec-core's code before rspec-core has been loaded.
-  if [ -f script/rspec_with_simplecov ]; then
+  if [ -f script/rspec_with_simplecov ] && is_mri; then
     rspec_bin=script/rspec_with_simplecov
   fi;