added Photo to Attachment.getForExt()

src/main/java/de/mrbesen/telegram/MessageBuilder.java

@@ -256,6 +256,8 @@ public class MessageBuilder {
 				return Attachment.Audio;
 			} else if(extention.equalsIgnoreCase("ogg")) {
 				return Attachment.Voice;
+			} else if(extention.equalsIgnoreCase("jpg") || extention.equalsIgnoreCase("jpeg") || extention.equalsIgnoreCase("png")) {
+				return Attachment.Photo;
 			}
 			return Attachment.Document;
 		}