Don't fail the pipeline when a colon-emoji is used

A colon-emoji like 💯 can be valid in the case where we're talking
about the GitLab feature that processes these into emojis. It's fine to
warn about those, but failing the pipeline is too restrictive.

danger/commit_messages/Dangerfile

@@ -163,10 +163,10 @@ def lint_commit(commit)
   end
 
   if emoji_checker.includes_emoji?(commit.message)
-    fail_commit(
+    warn_commit(
       commit,
       'Avoid the use of Markdown Emoji such as `:+1:`. ' \
-        'These add no value to the commit message, ' \
+        'These add limited value to the commit message, ' \
         'and are displayed as plain text outside of GitLab'
     )