Monika: polyfill `String.prototype.repeat` if necessary

Closes #25
Resolves Sentry issue SPNATI-4J

opponents/monika/js/monika.js

 if(!monika) var monika = (function (root) {
 
+/* Polyfill String.prototype.repeat */
+if (!String.prototype.repeat) {
+    String.prototype.repeat = function (count) {
+        'use strict';
+        if (this == null)
+            throw new TypeError('can\'t convert ' + this + ' to object');
+
+        var str = '' + this;
+        // To convert string to integer.
+        count = +count;
+        // Check NaN
+        if (count != count)
+            count = 0;
+
+        if (count < 0)
+            throw new RangeError('repeat count must be non-negative');
+
+        if (count == Infinity)
+            throw new RangeError('repeat count must be less than infinity');
+
+        count = Math.floor(count);
+        if (str.length == 0 || count == 0)
+            return '';
+
+        // Ensuring count is a 31-bit integer allows us to heavily optimize the
+        // main part. But anyway, most current (August 2014) browsers can't handle
+        // strings 1 << 28 chars or longer, so:
+        if (str.length * count >= 1 << 28)
+            throw new RangeError('repeat count must not overflow maximum string size');
+
+        var maxCount = str.length * count;
+        count = Math.floor(Math.log(count) / Math.log(2));
+        while (count) {
+            str += str;
+            count--;
+        }
+        str += str.substring(0, maxCount - str.length);
+        return str;
+    }
+}
+
 var exports = {};
 
 if (root.SENTRY_INITIALIZED) {