Update Drupal to 8.8.0 and use drupal/core-recommended instead of webflo/drupal-core-strict

composer.json

@@ -9,7 +9,7 @@
         "behat/behat": "^3.4",
         "behat/mink": "^1.7",
         "behat/mink-goutte-driver": "^1.2",
-        "composer/installers": "^1.0",
+        "composer/installers": "^1.7",
         "cweagans/composer-patches": "^1.0",
         "drupal-composer/drupal-scaffold": "^2.0.0",
         "drupal/allowed_formats": "^1.1",
@@ -18,7 +18,7 @@
         "drupal/ckeditor_markdown": "^1.1",
         "drupal/coffee": "1.x-dev",
         "drupal/comment_notify": "dev-1.x",
-        "drupal/core": "^8.6.2",
+        "drupal/core-recommended": "^8.8",
         "drupal/customerror": "1.x-dev",
         "drupal/diff": "^1.0@RC",
         "drupal/dropdown_language": "^2.2",