Add support for php 7.4

Author: snapshotpl

.travis.yml

@@ -26,6 +26,12 @@ matrix:
     - php: 7.3
       sudo: false
       env: SYMFONY_VERSION=4.2.* UNIT_TESTS=true
+    - php: 7.4snapshot
+      sudo: false
+      env: SYMFONY_VERSION=4.1.* UNIT_TESTS=true
+    - php: 7.4snapshot
+      sudo: false
+      env: SYMFONY_VERSION=4.2.* UNIT_TESTS=true
     - php: 7.1
       services: docker
       sudo: required
@@ -66,12 +72,12 @@ script:
     - if [ "$UNIT_TESTS" = true ]; then bin/phpunit --exclude-group=functional; fi
     - if [ "$FUNCTIONAL_TESTS" = true ]; then bin/test.sh --exclude-group=rdkafka; fi
     - if [ "RDKAFKA_TESTS" = true ]; then bin/test.sh --group=rdkafka; fi
-    
+
 notifications:
   webhooks:
     urls:
       - https://webhooks.gitter.im/e/3f8b3668e7792de23a49
-    on_success: change  
-    on_failure: always  
-    on_start: never     
+    on_success: change
+    on_failure: always
+    on_start: never