Fix bug in comment requirement

Previously, running a cap command like:

cap env deploy -s comment_value=foobar

would not work, as comment_value would error out with a LocalJumpError.
This patch fixes that issue.

Tested with:

cap env deploy (interactive)
cap env deploy -s comment_value=foobar (noninteractive)

successfully.

(Reminder to commenters: this is a public repo)
Merge pull request #18 from PagerDuty/fix-comment-logic

Fix bug in comment requirement