Update scalac_plugin_args call to the new option name.
Review Request #3132 - Created Nov. 16, 2015 and submitted
We updated the flag name but missed the option call.
This was failing internally because the flag didn't exist.
The ci run is in the queue but compiles that were failing with:18:15:18 00:43 [compile] 18:15:18 00:43 [compile] compile(src/jvm/org/mindrot:bcrypt) failed: plugin_args
now are compiling.