.travis.yml: use single quotes.

Should be in 381c491 commit.

No functional changes.

Author: php-coder

.travis.yml

@@ -39,9 +39,9 @@ after_failure:
   # In order to be able debug robot framework test flakes we need to have a report.
   # Just encode it to a gzipped binary form and dump to console.
   - if fgrep -qs 'status="FAIL"' target/robotframework-reports/output.xml; then
-      echo "===== REPORT START =====";
+      echo '===== REPORT START =====';
       cat target/robotframework-reports/output.xml | gzip -c | base64;
-      echo "===== REPORT END =====";
+      echo '===== REPORT END =====';
       sleep 5;
     fi