Bump manager version in dockerfile

Author: mroote

docker/Dockerfile

@@ -4,7 +4,7 @@ FROM frolvlad/alpine-glibc
 MAINTAINER Mitch Roote <[email protected]>
 
 ENV FACTORIO_VERSION=latest \
-    MANAGER_VERSION=0.8.0 \
+    MANAGER_VERSION=0.8.1 \
     ADMIN_PASSWORD=factorio
 
 VOLUME /opt/factorio/saves /opt/factorio/mods /opt/factorio/config /security