Fixed a bug causing the Confirmation message sending to fail (#73)

* Fixed a bug causing the Confirmation message sending to fail

When the system-wide configuration of “Sender E-mail Address” was done as an environmental variable, that variable wasn’t resolved and the variable name was passed as a “from” e-mail address, which caused SwiftMailer to fail on e-mail addressa format validation.

* Removed unused import referring to a non-existing class

src/ContactFormExtensions.php

@@ -172,7 +172,7 @@ public function init()
                 $message = new Message();
                 $message->setTo($e->submission->fromEmail);
                 if (isset(App::mailSettings()->fromEmail)) {
-                    $message->setFrom(App::mailSettings()->fromEmail);
+                    $message->setFrom(Craft::parseEnv(App::mailSettings()->fromEmail));
                 } else {
                     $message->setFrom($e->message->getTo());
                 }