add libpq-dev to production image

Author: jordanstephens

samples/rails/app/Dockerfile

@@ -18,7 +18,7 @@ FROM base as build
 
 # Install packages needed to build gems
 RUN apt-get update -qq && \
-    apt-get install --no-install-recommends -y build-essential git libvips pkg-config
+    apt-get install --no-install-recommends -y build-essential git libvips pkg-config libpq-dev
 
 # Set bundler config to force ruby platform
 RUN bundle config set force_ruby_platform true