Adds /var/www/discourse as a safe git directory.

Dockerfile

@@ -20,7 +20,8 @@ RUN apt-get update && apt-get install -y jq
 
 WORKDIR /var/www/discourse
 
-RUN git remote set-branches --add origin ${DISCOURSE_VERSION} &&\
+RUN git config --global --add safe.directory /var/www/discourse &&\
+    git remote set-branches --add origin ${DISCOURSE_VERSION} &&\
     git fetch --depth 1 origin ${DISCOURSE_VERSION} &&\
     sudo -u discourse bundle config --local deployment true &&\
     sudo -u discourse bundle config --local path ./vendor/bundle &&\