Travis: Ignore endroid/qr-code in a try to make PHP 7.4 tests working

Travis' PHP 7.4 build does not have php-gd available yet.

.travis.yml

@@ -23,6 +23,7 @@ cache:
 install:
   - if [ "$CODE_COVERAGE" != 1 ]; then phpenv config-rm xdebug.ini || true; fi
   - cp composer.json-dist composer.json
+  - composer remove endroid/qr-code --no-update
   - composer install --prefer-dist
 
 script: