Update PHP SDK dependency to latest version

This allows for the service account credentials to
be stored as strings in environment variables
parsed for during auto discovery.

Author: jeromegamez

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+* Updated `kreait/firebase-php` to `^4.40.1`
 * Added support for Laravel/Lumen `^7.0`
 
 ## 1.4.0 - 2020-02-22

composer.json

@@ -11,7 +11,7 @@
         }
     ],
     "require": {
-        "kreait/firebase-php": "^4.40.0",
+        "kreait/firebase-php": "^4.40.1",
         "illuminate/contracts": "^5.8|^6.0|^7.0",
         "illuminate/support": "^5.8|^6.0|^7.0"
     },