Fix search engines not indexing the site

Problem:
Lighthouse reports search engines can't index the site because noindex,
nofollow are in the meta robots tag.

Solution:
Set the hugo environment to production.

Result:
Lighthouse score improves.

Author: jeffmccune

Dockerfile.nginx

@@ -5,7 +5,9 @@ RUN apk add git && \
 
 COPY . /src/
 
-RUN hugo
+ENV HUGO_ENV="production"
+
+RUN hugo --gc
 
 FROM nginx:stable