Update changelog about --enable-coverage

Cabal/changelog

 -*-change-log-*-
 
+1.21.x (current development version)
+	* Replace --enable-library-coverage with --enable-coverage, which
+	enables program coverage for all components.
+
 1.20.0.1 Johan Tibell <johan.tibell@gmail.com> May 2014
 	* Fix streaming test output.
 
@@ -29,10 +33,6 @@
 	* Add test flag --show-details=streaming for real-time test output
 	* Add exec command
 
-1.11.x (current development version)
-
-1.10.0.x (next stable release version)
-
 1.10.2.0 Duncan Coutts <duncan@community.haskell.org> June 2011
 	* Include test suites in cabal sdist
 	* Fix for conditionals in test suite stanzas in .cabal files