Fix bug calculating a group's port

In the original foreman, an increase of 100 defined the number of the first process of the next group, hence, a two type Procfile uses ports 5000 and 5100. Forego was correctly printing this expected numbers but line 86 was recalculating this port number again with a distance of 1000 not a hundred. The result was that I was seeing my second type of process listening on port 6000, not the expected 5100.
Merge pull request #22 from davidpelaez/master

Fix bug calculating a group's port