Add support for tag/release tests

Author: wigman

.travis/before_script.sh

@@ -24,8 +24,13 @@ cd magento2
 # add composer package under test, composer require will trigger update/install
 composer config minimum-stability dev
 composer config repositories.travis_to_test git https://github.com/$TRAVIS_REPO_SLUG.git
-#TODO make it work with tags as well:
-composer require ${COMPOSER_PACKAGE_NAME}:dev-${TRAVIS_BRANCH}\#{$TRAVIS_COMMIT}
+
+if [ ! -z $TRAVIS_TAG  ]
+then
+    composer require ${COMPOSER_PACKAGE_NAME}:${TRAVIS_TAG}
+else
+    composer require ${COMPOSER_PACKAGE_NAME}:dev-${TRAVIS_BRANCH}\#${TRAVIS_COMMIT}
+fi
 
 # prepare for test suite
 case $TEST_SUITE in