Test migration to jest by hand

Apparently using regular expressions is way easier.

test/gcd/gcd.js

@@ -0,0 +1,5 @@
+const gcd = (...arr) => {
+const _gcd = (x, y) => (!y ? x : gcd(y, x % y));
+return [...arr].reduce((a, b) => _gcd(a, b));
+};
+module.exports = gcd;