Embedding SVG Images in Apple Mail (#53)

Apple Mail for example has a problem displaying svg images with the content-type image/svg. It musst be called image/svg+xml. Correcting this here. Should not be a problem for other mailers.

Author: urshofer

src/Mail/Message.php

@@ -303,6 +303,8 @@ private function createAttachment(string $file, string $content = null, string $
 		}
 		if (!strcasecmp($contentType, 'message/rfc822')) { // not allowed for attached files
 			$contentType = 'application/octet-stream';
+		} elseif (!strcasecmp($contentType, 'image/svg')) { // Troublesome for some mailers...
+			$contentType = 'image/svg+xml';
 		}
 
 		$part->setBody($content);