also relax SDK dependency to allow 5.x

Author: eli-darkly

composer.json

@@ -22,7 +22,7 @@
     "require": {
         "php": ">=7.3",
         "predis/predis": ">=1.0.0 <3.0.0",
-        "launchdarkly/server-sdk": "^4"
+        "launchdarkly/server-sdk": ">=4.0.0 <6.0.0"
     },
     "require-dev": {
         "launchdarkly/server-sdk-shared-tests": "@dev",