add some packages

node_modules/core-js/modules/_string-at.js

@@ -0,0 +1,17 @@
+var toInteger = require('./_to-integer');
+var defined = require('./_defined');
+// true  -> String#at
+// false -> String#codePointAt
+module.exports = function (TO_STRING) {
+  return function (that, pos) {
+    var s = String(defined(that));
+    var i = toInteger(pos);
+    var l = s.length;
+    var a, b;
+    if (i < 0 || i >= l) return TO_STRING ? '' : undefined;
+    a = s.charCodeAt(i);
+    return a < 0xd800 || a > 0xdbff || i + 1 === l || (b = s.charCodeAt(i + 1)) < 0xdc00 || b > 0xdfff
+      ? TO_STRING ? s.charAt(i) : a
+      : TO_STRING ? s.slice(i, i + 2) : (a - 0xd800 << 10) + (b - 0xdc00) + 0x10000;
+  };
+};