build: narrow ckeditor/ckeditor version constraint

Versions above 4.22.1 are LTS and no longer free.
Versions below 4.16.0 may not work correctly.

composer.json

@@ -17,7 +17,7 @@
   "require": {
     "quiqqer\/quiqqer": "*",
     "quiqqer\/qui": ">=1|*@dev",
-    "ckeditor\/ckeditor": "4.*"
+    "ckeditor\/ckeditor": ">=4.16.0 <=4.22.1"
   },
   "autoload": {
     "psr-4": {