JWT version bump (#552)

Author: ercsctt

composer.json

@@ -31,7 +31,7 @@
     "psr/http-client-implementation": "^1.0",
     "vonage/nexmo-bridge": "^0.1.0",
     "psr/log": "^1.1|^2.0|^3.0",
-    "vonage/jwt": "^0.5.0"
+    "vonage/jwt": "^0.6.0"
   },
   "require-dev": {
     "guzzlehttp/guzzle": ">=6",