fix a typo [ci skip]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54512 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -148,7 +148,7 @@ Fri Apr  1 20:58:33 2016  Martin Duerst  <duerst@it.aoyama.ac.jp>
 	* enc/unicode/case-folding.rb, casefold.h: Data generation to implement
 	  swapcase functionality for titlecase characters. Swapcase isn't defined
 	  by Unicode, because the purpose/usage of swapcase is unclear anyway.
-	  The implementation follows a proposal from Nobu, swaping the case of
+	  The implementation follows a proposal from Nobu, swapping the case of
 	  each component of a titlecase character individually.
 	  This means that the titlecase characters have to be decomposed.