do not upgrade RubyGems

Author: fxn

bootstrap.sh

@@ -32,8 +32,9 @@ install Ruby ruby2.5 ruby2.5-dev
 update-alternatives --set ruby /usr/bin/ruby2.5 >/dev/null 2>&1
 update-alternatives --set gem /usr/bin/gem2.5 >/dev/null 2>&1
 
-echo installing current RubyGems
-gem update --system -N >/dev/null 2>&1
+# FIXME: Do not upgrade RubyGems, see https://github.com/rails/rails-dev-box/issues/147.
+# echo installing current RubyGems
+# gem update --system -N >/dev/null 2>&1
 
 echo installing Bundler
 gem install bundler -N >/dev/null 2>&1