fix dependencies

Author: pfefferle

composer.json

@@ -4,7 +4,7 @@
     "type": "wordpress-plugin",
     "require": {
         "php": ">=5.6.0",
-        "composer/installers": "~2.0"
+        "composer/installers": "^1.0 || ^2.0"
     },
     "require-dev": {
         "phpunit/phpunit": "^5.7.21 || ^6.5 || ^7.5 || ^8",