Bazel: Tidy up gerrit_js_bundle rule
Bazel: Tidy up gerrit_js_bundle rule

Fix a typo and use some variables to avoid repetitions.

Change-Id: I9b3e757717a64e8538d5d05bdb86b3b26c9f363d

GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit