Bug 502625 - Explicitly require Email::Sender::Simple

I had assumed Email::Sender::Simple was bundled into Email::Sender.. it
appears that's not the case?

Author: mrenvoize

cpanfile

@@ -28,6 +28,7 @@ requires 'EV', '4.0';
 requires 'Email::Address::XS', '1.05';
 requires 'Email::MIME', '1.904';
 requires 'Email::Sender', '2.600';
+requires 'Email::Sender::Simple', '2.600';
 requires 'FFI::Platypus';
 requires 'File::MimeInfo::Magic';
 requires 'Future', '0.34';