Don't force RAILS_ENV in dockerfile

Dockerfile

@@ -38,8 +38,6 @@ RUN rails assets:precompile && \
 ################################################################################
 FROM base AS dev
 
-ENV RAILS_ENV=development
-
 COPY --from=builder /usr/local/bundle/ /usr/local/bundle/
 COPY --from=builder /app/ /app/
 COPY --from=builder /var/cache/app/ /app/