Running verilator broken if port name contains dutname as substring (#171)

* Running verilator broken if port name contains dutname as substring
Changed replace to replaceFirst to only change the dutname
in constructing verilator io interface
Changed GCDSpec port names to trigger the bug and verify fix.

* Removed main from RealGCD2.
Main was launching interpreter-repl,
IntelliJ doesn't like main's mixed with tests
And the chisel-template has better examples of how
to do this.