allows for firebase 5.0 (#1258)

Author: bshaffer

composer.json

@@ -9,7 +9,7 @@
         "php": ">=5.4",
         "google/auth": "^1.0",
         "google/apiclient-services": "^0.12",
-        "firebase/php-jwt": "~2.0|~3.0|~4.0",
+        "firebase/php-jwt": "~2.0|~3.0|~4.0|~5.0",
         "monolog/monolog": "^1.17",
         "phpseclib/phpseclib": "~0.3.10|~2.0",
         "guzzlehttp/guzzle": "~5.3.1|~6.0",