ci: fix branch comparison

Author: filipesilva

scripts/test-commit-messages.js

@@ -36,8 +36,9 @@ execSync('git fetch origin');
 // Travis doesn't have master when running jobs on other branches (minor/patch/etc).
 execSync('git fetch origin master:master');
 
+const branch = process.env.TRAVIS_BRANCH;
 
-const output = execSync('git log master.. --reverse --format="%H %s" --no-merges', {
+const output = execSync('git log ' + branch + '..HEAD --reverse --format="%H %s" --no-merges', {
   encoding: 'utf-8'
 });