optimized container building

* merged all npm -g install and npm link commands
* from now on, docker should only generate 2 images, instead
of one for each npm install or npm link call

Dockerfile

@@ -26,32 +26,33 @@ COPY .eslintrc .eslintrc
 COPY index.html index.html
 COPY package.json package.json
 
-RUN npm -g install babel-core
-RUN npm -g install babel-eslint
-RUN npm -g install babel-loader
-RUN npm -g install babel-preset-es2015
-RUN npm -g install babel-preset-react
-RUN npm -g install eslint
-RUN npm -g install eslint-plugin-react
-RUN npm -g install eslint-loader
-RUN npm -g install gulp
-RUN npm -g install gulp-babel
-RUN npm -g install gulp-util
-RUN npm -g install webpack
-RUN npm -g install webpack-dev-server
-
-RUN npm link babel-core
-RUN npm link babel-eslint
-RUN npm link babel-loader
-RUN npm link babel-preset-es2015
-RUN npm link babel-preset-react
-RUN npm link eslint
-RUN npm link eslint-plugin-react
-RUN npm link eslint-loader
-RUN npm link gulp
-RUN npm link gulp-babel
-RUN npm link gulp-util
-RUN npm link webpack
-RUN npm link webpack-dev-server
+RUN npm -g install babel-core \
+    babel-eslint \
+    babel-eslint \
+    babel-loader \
+    babel-preset-es2015 \
+    babel-preset-react \
+    eslint \
+    eslint-plugin-react \
+    eslint-loader \
+    gulp \
+    gulp-babel \
+    gulp-util \
+    webpack \
+    webpack-dev-server
+
+RUN npm link babel-core \
+    babel-eslint \
+    babel-loader \
+    babel-preset-es2015 \
+    babel-preset-react \
+    eslint \
+    eslint-plugin-react \
+    eslint-loader \
+    gulp \
+    gulp-babel \
+    gulp-util \
+    webpack \
+    webpack-dev-server
 
 CMD ["/node.sh"]