Remove unnecessary docker config

mrfusion already respects the PORT env var. No need to specify it.

After this commit, however, you will need to specify exposing the port
on the CLI when starting the container.

Heroku providers the PORT when it runs the container.

Signed-off-by: Kevin Fitzpatrick <kevin@influxdb.com>

Dockerfile

@@ -6,8 +6,4 @@ RUN apk add --update ca-certificates && \
 
 ADD mrfusion /mrfusion
 
-EXPOSE 8888
+CMD ["/mrfusion"]
-
-# ENV PORT ||= 8888
-
-CMD ["/mrfusion", "--port=$PORT"]