fix: added phpunit version constrain for higher php versions

Author: prisis

.travis.yml

@@ -47,21 +47,21 @@ matrix:
         - php: 7.1
           env: SYMFONY_PHPUNIT_VERSION="6.3"
         - php: 7.2
-          env: COVERAGE=true TEST_COMMAND="composer test-ci"
+          env: COVERAGE=true TEST_COMMAND="composer test-ci" SYMFONY_PHPUNIT_VERSION="6.3"
         - php: 7.2
-          env: COVERAGE=true TEST_COMMAND="composer test-ci"
+          env: COVERAGE=true TEST_COMMAND="composer test-ci" SYMFONY_PHPUNIT_VERSION="6.3"
 
           # Test LTS versions
         - php: 7.3
-          env: DEPENDENCIES="dunglas/symfony-lock:^2"
+          env: DEPENDENCIES="dunglas/symfony-lock:^2" SYMFONY_PHPUNIT_VERSION="6.3"
         - php: 7.3
-          env: DEPENDENCIES="dunglas/symfony-lock:^3"
+          env: DEPENDENCIES="dunglas/symfony-lock:^3" SYMFONY_PHPUNIT_VERSION="6.3"
         - php: 7.3
-          env: DEPENDENCIES="dunglas/symfony-lock:^4"
+          env: DEPENDENCIES="dunglas/symfony-lock:^4" SYMFONY_PHPUNIT_VERSION="6.3"
 
           # Latest commit to master
         - php: 7.3
-          env: STABILITY="dev"
+          env: STABILITY="dev" SYMFONY_PHPUNIT_VERSION="6.3"
 
     allow_failures:
           # dev stability is allowed to fail.