Do not cache regex after first use

The /o flag tells Ruby to only interpolate the regex once, cache the
result of that interpolation, and use it for the rest of the life of the
project. Effectively, it in-lines the result of the first time you
interpolate. This is a Bad Time™️ for us because that means we cache the
first story number we try. In most production usages this is fine b/c we
fire up the Ruby process and only check a single time. But that's not
true for tests, so depending on the order tests are run, they could
start breaking!

No more!

Author: stevenharman

lib/git_tracker/commit_message.rb

@@ -6,7 +6,7 @@ def initialize(file)
     end
 
     def mentions_story?(number)
-      @message =~ /^(?!#).*\[(\w+\s)?(#\d+\s)*##{number}(\s#\d+)*(\s\w+)?\]/io
+      @message =~ /^(?!#).*\[(\w+\s)?(#\d+\s)*##{number}(\s#\d+)*(\s\w+)?\]/i
     end
 
     def keyword