Also bump version in copyright header

Makefile

@@ -80,6 +80,7 @@ po2json:
 
 .PHONY: release
 release:
+	$(SED) -ri s/Version:\ [0-9]\+\.[0-9]\+\.[0-9]\+/Version:\ $(VERSION)/ COPYRIGHT
 	$(SED) -ri s/Version:\ [0-9]\+\.[0-9]\+\.[0-9]\+/Version:\ $(VERSION)/ src/start.frag
 	$(SED) -ri s/Project-Id-Version:\ Converse\.js\ [0-9]\+\.[0-9]\+\.[0-9]\+/Project-Id-Version:\ Converse.js\ $(VERSION)/ locale/converse.pot
 	$(SED) -ri s/\"version\":\ \"[0-9]\+\.[0-9]\+\.[0-9]\+\"/\"version\":\ \"$(VERSION)\"/ bower.json