Use proper script way to clone Emoji files from www

Differential Revision: D5615872

fbshipit-source-id: 7f2c19f1a65f42b78136be7e6a608d0415c1a49f

Libraries/polyfills/String.prototype.es6.js

@@ -92,3 +92,39 @@ if (!String.prototype.includes) {
     }
   };
 }
+
+if (!String.prototype.codePointAt) {
+  String.prototype.codePointAt = function(position) {
+    if (this == null) {
+      throw TypeError();
+    }
+    var string = String(this);
+    var size = string.length;
+    // `ToInteger`
+    var index = position ? Number(position) : 0;
+    if (Number.isNaN(index)) {
+      index = 0;
+    }
+    // Account for out-of-bounds indices:
+    if (index < 0 || index >= size) {
+      return undefined;
+    }
+    // Get the first code unit
+    var first = string.charCodeAt(index);
+    var second;
+    if (
+      // check if it’s the start of a surrogate pair
+      first >= 0xd800 &&
+      first <= 0xdbff && // high surrogate
+      size > index + 1 // there is a next code unit
+    ) {
+      second = string.charCodeAt(index + 1);
+      if (second >= 0xdc00 && second <= 0xdfff) {
+        // low surrogate
+        // http://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
+        return (first - 0xd800) * 0x400 + second - 0xdc00 + 0x10000;
+      }
+    }
+    return first;
+  };
+}