Make entrypoint.sh the entrypoint.

Eventhou it is the ENTRYPOINT, it will just work
as if it was the CMD because it exec all arguments.

Dockerfile

@@ -21,4 +21,5 @@ USER ngrok
 
 EXPOSE 4040
 
-CMD ["/entrypoint.sh"]
+ENTRYPOINT ["/entrypoint.sh"]
+CMD ["/bin/ngrok"]

entrypoint.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/sh -e
 
 if [ "$1" = "/bin/sh" ]; then
   shift
@@ -55,4 +55,4 @@ case "$1" in
   *)        ARGS="$PROTOCOL $ARGS -log stdout $* $FWD" ;;
 esac
 
-exec /bin/ngrok $ARGS
+exec "$@"