minor #997 Updated the Travis config (javiereguiluz)

This PR was squashed before being merged into the master branch (closes #997).

Discussion
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Updated the Travis config

Commits
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42fc1d3 Updated the Travis config

Author: javiereguiluz

.travis.yml

@@ -18,12 +18,13 @@ matrix:
     - php: 7.1.18
     - php: 7.2
     - php: 7.3
-    - php: nightly
+    # 'php: nightly' is PHP 8.0
+    - php: 7.4snapshot
   allow_failures:
-    - php: nightly
+    - php: 7.4snapshot
 
 before_install:
-  - '[[ "$TRAVIS_PHP_VERSION" == "nightly" ]] || phpenv config-rm xdebug.ini'
+  - '[[ "$TRAVIS_PHP_VERSION" == "7.4snapshot" ]] || phpenv config-rm xdebug.ini'
   - composer self-update
 
 install:
@@ -33,7 +34,7 @@ install:
 script:
   - ./bin/phpunit
   # this checks that the source code follows the Symfony Code Syntax rules
-  - '[[ "$TRAVIS_PHP_VERSION" == "nightly" ]] || ./vendor/bin/php-cs-fixer fix --diff --dry-run -v'
+  - '[[ "$TRAVIS_PHP_VERSION" == "7.4snapshot" ]] || ./vendor/bin/php-cs-fixer fix --diff --dry-run -v'
   # this checks that the YAML config files contain no syntax errors
   - ./bin/console lint:yaml config
   # this checks that the Twig template files contain no syntax errors