Merge pull request #115 from localheinz/feature/php7.3

Enhancement: Add PHP 7.3 to Travis CI build matrix

.travis.yml

@@ -71,6 +71,7 @@ jobs:
         - if [[ -n "$GITHUB_TOKEN" ]]; then composer config github-oauth.github.com $GITHUB_TOKEN; fi
 
       install:
+        - if [[ "$TRAVIS_PHP_VERSION" == "7.3" ]]; then composer remove --dev localheinz/php-cs-fixer-config; fi
         - if [[ "$WITH_LOWEST" == "true" ]]; then composer update --prefer-lowest; fi
         - if [[ "$WITH_LOCKED" == "true" ]]; then composer install; fi
         - if [[ "$WITH_HIGHEST" == "true" ]]; then composer update; fi
@@ -114,6 +115,24 @@ jobs:
 
       env: WITH_HIGHEST=true
 
+    - <<: *TEST
+
+      php: 7.3
+
+      env: WITH_LOWEST=true
+
+    - <<: *TEST
+
+      php: 7.3
+
+      env: WITH_LOCKED=true
+
+    - <<: *TEST
+
+      php: 7.3
+
+      env: WITH_HIGHEST=true
+
     - stage: Infection
 
       php: 7.2