upgrade to latest sentry/sentry

Author: markushausammann

composer.json

@@ -14,7 +14,7 @@
     ],
     "require": {
         "php": "^5.5 || ^7.0",
-        "sentry/sentry": "0.16.0"
+        "sentry/sentry": "0.21.2"
     },
     "conflict": {
         "zendframework/zendframework": "<2.5.3"