fix: Add missing concat helper.

Author: chriseppstein

Diff for: packages/@css-blocks/ember/runtime/app/helpers/-css-blocks-concat.ts

@@ -0,0 +1,12 @@
+/// @ts-ignore
+import { helper } from "@ember/component/helper";
+
+// tslint:disable-next-line:prefer-unknown-to-any
+function _concat(args: any[]) {
+  return args.join("");
+}
+
+const concat = helper(_concat);
+
+// tslint:disable-next-line:no-default-export
+export default concat;