bugfix: sha2 must return Uint8Array, not ArrayBuffer

lib/browser/sha2.js

@@ -9,5 +9,7 @@ sha2.sum = function (alg, str) {
 		data = encoder.encode(str);
 	}
 	var sha = 'SHA-' + String(alg).replace(/^sha-?/i, '');
-	return window.crypto.subtle.digest(sha, data);
+	return window.crypto.subtle.digest(sha, data).then(function (buf) {
+		return new Uint8Array(buf);
+	});
 };