travis: uses PHP 7.4 for coding checks

Author: dg

Diff for: .travis.yml

@@ -27,13 +27,15 @@ jobs:
 
 
         -   name: Nette Code Checker
+            php: 7.4
             install:
                 - travis_retry composer create-project nette/code-checker temp/code-checker ^3 --no-progress
             script:
                 - php temp/code-checker/code-checker --strict-types
 
 
         -   name: Nette Coding Standard
+            php: 7.4
             install:
                 - travis_retry composer create-project nette/coding-standard temp/coding-standard ^2 --no-progress
             script:
@@ -54,11 +56,13 @@ jobs:
 
 
         -   stage: Static Analysis (informative)
+            php: 7.4
             script:
                 - composer run-script phpstan
 
 
         -   stage: Code Coverage
+            php: 7.4
             script:
                 - vendor/bin/tester -p phpdbg tests -s --coverage ./coverage.xml --coverage-src ./src
             after_script: