merge revision(s) 53320,54756: [Backport #12246]
* doc/extension.rdoc: [DOC] `nul` should be uppercase. change 'nul' => 'NUL'. [Fix GH-1172] * doc/extension.rdoc: Improvements to english grammers. [Bug #12246][ruby-core:74792][ci skip]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@54766 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
merge revision(s) 53320,54756: [Backport #12246]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@54766 b2dd03c8-39d4-4d8f-98ff-823fe69b080e