Bump dependency versions

Bump Braintree PHP to 3.31.0
Bump Braintre Drop-in to 1.10.0

Author: Timothy Martinak

composer.json

@@ -1,6 +1,6 @@
 {
   "require" : {
-    "braintree/braintree_php" : "3.30.0",
+    "braintree/braintree_php" : "3.31.0",
     "php": ">=5.2.1",
     "vlucas/phpdotenv": "2.1.0"
   },

composer.lock

@@ -36,7 +36,7 @@
         </div>
     </div>
 
-    <script src="https://js.braintreegateway.com/web/dropin/1.9.4/js/dropin.min.js"></script>
+    <script src="https://js.braintreegateway.com/web/dropin/1.10.0/js/dropin.min.js"></script>
     <script>
         var form = document.querySelector('#payment-form');
         var client_token = "<?php echo($gateway->ClientToken()->generate()); ?>";