fix(DEV): add global node-sass

This fixes the case, where you bind-mount your own tileboard source directory into the dev container.

Apparently, the node-sass module is compiled for the specdific machine.
This seems to result in the `node-sass` executable not being found in the container, if the `node_modules` folder was compiled on a different machine (OS?).
By adding node-sass globally in the container, it can be found even with a bind-mounted `tileboard-source` directory.

Dockerfile.nightly

@@ -12,6 +12,7 @@ RUN mkdir /tileboard-source \
  && mkdir /tileboard \
  && ln -s /tileboard build \
  && yarn install \
+ && npm install --global node-sass \
  && yarn run build
 
 # Start Server
@@ -31,4 +32,4 @@ COPY --from=dev /tileboard /tileboard
 # Start Server
 WORKDIR /tileboard
 EXPOSE  8000
-ENTRYPOINT python3 -m http.server
+ENTRYPOINT python3 -m http.server