Fix for debug argument syntax

I was getting the following error whenever I attempted to run SBT with the option `-jvm-debug 5005`:
```
Error occurred during initialization of VM
Could not find agent library jdwp:transport on the library path, with error: libjdwp:transport.so: cannot open shared object file: No such file or directory
```
It looks like this was due to a syntax error in the  debugger flag.