MAGETWO-82555: Travis: surround variable TRAVIS_BRANCH with double-quotes instead of single-quotes #11667

 - Merge Pull Request #11667 from adrian-martinez-interactiv4/magento2:FR#TRAVIS-BRANCH-SINGLE-TO-DOUBLE-QUOTES
 - Merged commits:
   1. e31d516

Author: Oleksii Korshenko

dev/travis/before_script.sh

@@ -71,7 +71,7 @@ case $TEST_SUITE in
             --output-file="$changed_files_ce" \
             --base-path="$TRAVIS_BUILD_DIR" \
             --repo='https://github.com/magento/magento2.git' \
-            --branch='$TRAVIS_BRANCH'
+            --branch="$TRAVIS_BRANCH"
         cat "$changed_files_ce" | sed 's/^/  + including /'
 
         cd ../../..