Update SignedRequest example to handle ValidationExceptions

If expected values are missing or invalid when calling createFromGlobals() an exception is thrown.
The example now demonstrates how an implementation can handle this and respond cleanly.

Author: chrisminett

examples/signedrequest-verification.php

@@ -6,7 +6,12 @@
 $requestValidator = new \MessageBird\RequestValidator('YOUR_SIGNING_KEY');
 
 // Set up the signed request from the PHP global variables.
-$request = \MessageBird\Objects\SignedRequest::createFromGlobals();
+try {
+    $request = \MessageBird\Objects\SignedRequest::createFromGlobals();
+} catch (\MessageBird\Exceptions\ValidationException $e) {
+    // The request was missing expected values, so respond accordingly.
+    http_response_code(412);
+}
 
 if (!$requestValidator->verify($request)) {
     // The request was invalid, so respond accordingly.