Fixes --dry-run returning "Unknown arguments"

It appears --dry-run didn't work at all, but its equivalent
argument, --test, does work. This seems to be a limitation of
docopt. Removing --dry-run should be backwards compatible since
it didn't work.
Merge pull request #324 from briancline/dry-run-a-little-too-dry

Fixes --dry-run returning "Unknown arguments"