ci: fix branch comparison

Author: filipesilva

scripts/test-commit-messages.js

@@ -37,7 +37,7 @@ execSync('git fetch origin');
 execSync('git fetch origin master:master');
 
 
-const output = execSync('git log master.. --reverse --format="%H %s" --no-merges', {
+const output = execSync(`git log ${TRAVIS_BRANCH}..HEAD --reverse --format="%H %s" --no-merges`, {
   encoding: 'utf-8'
 });