Fix conflict resolution mistake.

Author: martinemde

lib/rubygems/installer.rb

@@ -684,7 +684,7 @@ def process_options # :nodoc:
         # * `true`: `--user-install`
         # * `false`: `--no-user-install` and
         # * `nil`: option was not specified
-        if options[:user_install] || Gem.auto_user_install
+        if options[:user_install] || (options[:user_install].nil? && Gem.auto_user_install)
           @gem_home = Gem.user_dir
         end
       end