Reorder things a bit in theia docker file

concourse/theia-docker-image/Dockerfile

@@ -19,13 +19,16 @@ RUN mkdir /theia-app
 ADD package.json /theia-app
 WORKDIR /theia-app
 # using "NODE_OPTIONS=..." to avoid out-of-memory problem in CI
+
+
+ENV SHELL=/bin/bash \
+    THEIA_DEFAULT_PLUGINS=local-dir:/theia-app/plugins
+
+ADD plugins /theia-app/plugins
+
 RUN yarn --cache-folder ./ycache && rm -rf ./ycache && \
     NODE_OPTIONS="--max_old_space_size=8192" yarn theia build ; \
     yarn theia download:plugins
 
-ADD plugins /theia-app/plugins
-
-ENV SHELL=/bin/bash \
-    THEIA_DEFAULT_PLUGINS=local-dir:/theia-app/plugins
 ENTRYPOINT [ "yarn",  "theia", "start", "--hostname=0.0.0.0", "/home/project" ]
 EXPOSE 3000