Add eslint to the Dockerfile.

Dockerfile

@@ -7,11 +7,14 @@ ENV PACKAGES="\
     git \
     python=2.7.12-r0 \
     py-pip=8.1.2-r0 \
+    nodejs \
 "
 RUN apk --update add $PACKAGES && \
     rm -rf /var/cache/apk/* /tmp/* /var/tmp/*
 
 RUN pip install vim-vint==0.3.9
 
+RUN npm install -g eslint@3.7.1
+
 RUN git clone https://github.com/junegunn/vader.vim vader && \
     cd vader && git checkout c6243dd81c98350df4dec608fa972df98fa2a3af