[master] a minor grammar fix to changelog entry.

ChangeLog

 486.	[bug]*		jinmei
 	All public header files for libb10-dns++ are now installed.
 	Template configure.ac and utility AC macros for external projects
-	using the library is provided under the "examples" directory.
+	using the library are provided under the "examples" directory.
 	The src/bin/host was moved as part of the examples (and not
 	installed with other BIND 10 programs any more).
 	(Trac #1870, git 4973e638d354d8b56dcadf71123ef23c15662021)