Dockerfile.build: fix apk invocation

Use --no-cache flag to
 - avoid doing cache update;
 - leaving metadata in the resulting image).

Per https://github.com/gliderlabs/docker-alpine/blob/master/docs/usage.md#disabling-cache

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

Dockerfile.builder

@@ -8,7 +8,7 @@ RUN go get -d github.com/tdewolff/minify/cmd/minify \
 FROM starefossen/github-pages:177
 
 # Get some utilities we need for post-build steps
-RUN apk update && apk add bash wget subversion gzip
+RUN apk add --no-cache bash wget subversion gzip
 
 # Copy scripts used for static HTML post-processing.
 COPY scripts /scripts

Dockerfile.nginx.onbuild

@@ -16,4 +16,4 @@ ONBUILD COPY --from=builder /site /usr/share/nginx/html
 COPY nginx-overrides.conf /etc/nginx/conf.d/default.conf
 
 # Start Nginx to serve the archive at / (which will redirect to the version-specific dir)
-CMD echo -e "Docker docs are viewable at:\nhttp://0.0.0.0:4000"; exec nginx -g 'daemon off;'
+CMD echo -e "Docker docs are viewable at:\nhttp://0.0.0.0:4000"; exec nginx -g 'daemon off;'