Use conventional test syntax instead of magic "resolves"

Since there was another assertion in the test, and it did not actively
wait for the promise to be resolved, the test passed without evaluating
the second assertion.

tests/unit/client/init.spec.ts

@@ -33,7 +33,9 @@ describe( 'client/init', () => {
 		const termboxRequestPromise = init();
 
 		expect( termboxRequestPromise ).toBeInstanceOf( Promise );
-		expect( termboxRequestPromise ).resolves.toBeInstanceOf( TermboxRequest );
+		return termboxRequestPromise.then( ( request ) => {
+			expect( request ).toBeInstanceOf( TermboxRequest );
+		} );
 	} );
 
 	it( 'generates a TermboxRequest from the mw environment', () => {