link global npm node_modules directory to root in order to be an *real* global module

Dockerfile

@@ -33,11 +33,12 @@ RUN  npm --progress false install > /dev/null \
 COPY . .
 RUN npm --progress false link
 
-RUN mkdir /app
+# Loading from node_modules Folders: https://nodejs.org/api/modules.html
+# If it is not found there, then it moves to the parent directory, and so on, until the root of the file system is reached.
+RUN mkdir /app && ln -s /usr/local/lib/node_modules /
 VOLUME [ "/app" ]
 
 ENV TS_NODE_COMPILER_OPTIONS '{"target":"es6"}'
-ENV NODE_PATH /usr/local/lib/node_modules
 
 ENTRYPOINT [ "/wechaty/bin/entrypoint.sh" ]
 CMD [ "start" ]