neither Dockerfile nor Vagrant should actually install bundler these days

Dockerfile

@@ -29,7 +29,6 @@ RUN apk add --no-cache \
       git \
     && echo "gem: --no-ri --no-rdoc" > /etc/gemrc \
     && gem update --system \
-    && gem install bundler \
     && bundle install --clean --no-cache --system $BUNDLER_ARGS \
     # temp fix for https://github.com/bundler/bundler/issues/6680
     && rm -rf /usr/local/bundle/cache \

Vagrantfile

@@ -31,7 +31,6 @@ Vagrant.configure(2) do |config|
   [ "gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3",
     "curl -L https://get.rvm.io | bash -s stable",
     "source ~/.rvm/scripts/rvm && cd /vagrant && rvm install `cat .ruby-version`",
-    "source ~/.rvm/scripts/rvm && cd /vagrant && gem install bundler",
     "source ~/.rvm/scripts/rvm && cd /vagrant && bundle",
     "mkdir -p ~/.msf4",
   ].each do |step|