Make cockpit-starter-kit.spec.in rpmspec compliant

Use `%{VERSION}` as version macro instead of `@VERSION@`, so that the
.spec.in file is syntactically a correct spec file that can be parsed
with `rpmspec`.

Makefile

@@ -61,7 +61,7 @@ dist/po.%.js: po/%.po $(NODE_MODULES_TEST)
 #
 
 %.spec: %.spec.in
-	sed -e 's/@VERSION@/$(VERSION)/g' $< > $@
+	sed -e 's/%{VERSION}/$(VERSION)/g' $< > $@
 
 $(WEBPACK_TEST): $(NODE_MODULES_TEST) $(shell find src/ -type f) package.json webpack.config.js $(patsubst %,dist/po.%.js,$(LINGUAS))
 	NODE_ENV=$(NODE_ENV) npm run build

cockpit-starter-kit.spec.in

@@ -1,5 +1,5 @@
 Name: cockpit-starter-kit
-Version: @VERSION@
+Version: %{VERSION}
 Release: 1%{?dist}
 Summary: Cockpit Starter Kit Example Module
 License: LGPLv2+