Fix hugo environment for robots.txt in not-prod

Dockerfile.staging

@@ -1,10 +1,10 @@
 FROM rancher/docs:build as build
+ENV HUGO_ENV staging
 
 WORKDIR /run
 COPY gulpfile.babel.js /run/
 COPY .eslintrc.js /run/
 COPY config.toml /run/
-COPY netlify.toml /run/
 COPY archetypes archetypes
 COPY data data
 COPY layouts layouts
@@ -12,8 +12,6 @@ COPY scripts scripts
 COPY content content
 COPY src src
 
-ENV HUGO_ENV production
-
 ADD https://github.com/rancherlabs/website-theme/archive/master.tar.gz master.tar.gz
 RUN tar -xzf master.tar.gz --strip 1 -C /run/node_modules/rancher-website-theme && rm master.tar.gz