open-mpi 1.8.3: Fix the bin/vtsetup script

The `bin/vtsetup` script does not work, because `$bindir/vtsetup.jar` is expected to be a jar file, not a shell script.

```
❯❯❯ vtsetup
Error: Invalid or corrupt jarfile /usr/local/Cellar/open-mpi/1.8.3/bin/vtsetup.jar
```

I was basing that observation on the output of `brew options`. I was expecting to see `--with-java`.

```
❯❯❯ brew options open-mpi
--c++11
	Build using C++11 mode
--disable-fortran
	Do not build the Fortran bindings
--enable-mpi-thread-multiple
	Enable MPI_THREAD_MULTIPLE
```