fix(typedefs): do not require brand and application (#1264)

We don't always set both. For example, see [axe-webdriverjs](https://github.com/dequelabs/axe-webdriverjs/blob/v2.0.1/lib/axe-injector.js#L28).



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axe.d.ts

@@ -91,8 +91,8 @@ declare namespace axe {
 	}
 	interface Spec {
 		branding?: {
-			brand: string;
-			application: string;
+			brand?: string;
+			application?: string;
 		};
 		reporter?: ReporterVersion;
 		checks?: Check[];