create required directory to store nginx pid

Dockerfile

@@ -1,12 +1,13 @@
-FROM alpine:3.3
+FROM alpine:3.4
 
 MAINTAINER Roman Tarnavski
 
 RUN apk add --update nginx
+RUN mkdir -p /run/nginx
 
 COPY nginx.conf /etc/nginx/
 ADD ./dist/ /usr/share/nginx/html
 
 EXPOSE 8080
 
-CMD nginx -g 'daemon off;'
+CMD nginx -g 'daemon off;'