[BUILD] Add PHP 7.4 to travis build (#22)

.travis.yml

@@ -3,6 +3,7 @@ language: php
 php:
   - 7.2
   - 7.3
+  - 7.4
 
 sudo: false
 
@@ -29,25 +30,25 @@ matrix:
   fast_finish: true
   include:
     - stage: lint
-      php: 7.3
+      php: 7.4
       env: TARGET=lint
     - stage: lint
-      php: 7.3
+      php: 7.4
       env: TARGET=phpstan
     - stage: lint
-      php: 7.3
+      php: 7.4
       env: TARGET=checkdeps
     - stage: test
       php: 7.2
       env: COMPOSER_FLAGS="--prefer-lowest"
     - stage: test
-      php: 7.3
+      php: 7.4
       env: SYMFONY_VERSION=3.4.*
     - stage: test
-      php: 7.3
+      php: 7.4
       env: SYMFONY_VERSION=4.2.*
   allow_failures:
-    - php: 7.3
+    - php: 7.4
       env: TARGET=checkdeps
 
 before_install:

phpstan.neon.dist

@@ -13,3 +13,8 @@ parameters:
         - '#Cannot call method scalarNode\(\) on Symfony\\Component\\Config\\Definition\\Builder\\NodeParentInterface\|null.#'
         - "/Call to function method_exists.. with 'Symfony.+' and 'getRootNode' will always evaluate to false./"
 
+        -
+            message: "#^Call to an undefined method Symfony\\\\Component\\\\Config\\\\Definition\\\\Builder\\\\TreeBuilder::root\\(\\)\\.$#"
+            count: 1
+            path: src/DependencyInjection/Configuration.php
+