Merge pull request #4143 from rubygems/use-abort

Use `abort(message)` instead of `puts` and `exit`

(cherry picked from commit 46ec519)

Author: deivid-rodriguez

lib/rubygems/server.rb

@@ -431,8 +431,7 @@ def initialize(gem_dirs, port, daemon, launch = nil, addresses = nil)
     begin
       require 'webrick'
     rescue LoadError
-      puts "webrick is not found. You may need to `gem install webrick` to install webrick."
-      exit
+      abort "webrick is not found. You may need to `gem install webrick` to install webrick."
     end
 
     Gem::RDoc.load_rdoc