Adding PHP 7.4 testing, remove git diff test.

Author: grasmash

.travis.yml

@@ -3,6 +3,12 @@ language: php
 # @see https://pantheon.io/blog/highest-lowest-testing-multiple-symfony-versions
 matrix:
   include:
+    - php: 7.4
+      # Resolves to Symfony 5.
+      env: 'HIGHEST_LOWEST="update"'
+    - php: 7.3
+        # Resolves to Symfony 5.
+      env: 'HIGHEST_LOWEST="update"'
     - php: 7.2
       # Resolves to Symfony 5.
       env: 'HIGHEST_LOWEST="update"'
@@ -27,10 +33,6 @@ install:
   - composer validate --no-check-all --ansi
   - 'composer -n ${HIGHEST_LOWEST-install} --prefer-dist -o'
 
-before_script:
-  # Verify that no git diffs (caused by line ending variation) exist.
-  - git diff --exit-code
-
 script:
   - composer test