Move build order

Moving the .deb addition to after we install gnupg will prevent an
extra error from appearing. See #2

Dockerfile

@@ -10,9 +10,9 @@ FROM debian:latest
 
 MAINTAINER Mark Ide Jr (https://www.mide.io)
 
-RUN echo "deb http://overviewer.org/debian ./" >> /etc/apt/sources.list && \
-    apt-get update && \
+RUN apt-get update && \
     apt-get install -y wget gnupg && \
+    echo "deb http://overviewer.org/debian ./" >> /etc/apt/sources.list && \
     wget -O - https://overviewer.org/debian/overviewer.gpg.asc | apt-key add - && \
     apt-get update && \
     apt-get install -y minecraft-overviewer && \