* ruby.1: fixed typo.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@16064 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ruby.1

@@ -347,7 +347,7 @@ Disables (or enables) the specified
 .It Fl -enable-gems
 Disables (or enables) RubyGems libraries.  By default, Ruby will load the latest
 version of each installed gem. The
-.Li Gem::Enabled
+.Li Gem::Enable
 constant is true if RubyGems is enabled, false if otherwise.
 .Pp
 .It Fl -disable-rubyopt