[ruby-cvs:67217] nobu:r60036 (trunk): Fix a reference [ci skip]

[nobu at ruby-lang.org]

nobu	2017-09-27 08:28:06 +0900 (Wed, 27 Sep 2017)

  New Revision: 60036

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=60036

  Log:
    Fix a reference [ci skip]
    
    [Fix GH-1706]
    Author:    hkdnet <hkdnet at users.noreply.github.com>

  Modified files:
    trunk/doc/extension.ja.rdoc