Fix the --browse option in ruby >= 1.9

In newer rubies, the `browse` parameter shadows the outer variable, which is the one we actually want to set. The parameter wasn't being used, anyway.

Tested manually in `1.8.7-p371`, `1.9.3-p392`, and `2.0.0-p0`, since there aren't any tests for the `shotgun` binary and I'm not industrious enough to add them right now.