Replace --no-ri --no-rdoc with --no-document (#27)

Rubygems 3 is out and shipped in ruby:2.4/2.5 docker images by default.

Author: bcardiff

linux/Dockerfile-fpm

@@ -6,4 +6,4 @@ RUN apt-get update \
  && apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 
 ENV PATH="/usr/local/bundle/bin/:${PATH}"
-RUN gem install --no-ri --no-rdoc fpm -v 1.10.2
+RUN gem install --no-document fpm -v 1.10.2