Updated interface version to 50300 for patch 5.3.

diff --git a/KillTrack.toc b/KillTrack.toc
index f6edaf7..80b7784 100644
--- a/KillTrack.toc
+++ b/KillTrack.toc
@@ -1,4 +1,4 @@
-## Interface: 50200
+## Interface: 50300
 ## Version: @project-version@
 ## Title: KillTrack
 ## Notes: Keeps track of how many kills you have per mob and displays them in a list.