Shut up meteor without causing syntax errors

Apperently the METEOR_ALLOW_SUPERUSER is interpreted as javascript code or
something like that.

Dockerfile.meteor

 FROM debian:bullseye
 
 ENV METEOR_VERSION=2.5.1
-ENV METEOR_ALLOW_SUPERUSER=yes
+ENV METEOR_ALLOW_SUPERUSER=true
 
 RUN apt-get -qq update && \
     apt-get -qq dist-upgrade && \