FIX: Add `String.includes` polyfill for IE11

app/assets/javascripts/polyfills.js

@@ -94,4 +94,21 @@ if (!Array.prototype.includes) {
     }
   });
 }
+
+// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/includes#Polyfill
+if (!String.prototype.includes) {
+  Object.defineProperty(String.prototype, 'includes', {
+    value: function(search, start) {
+      if (typeof start !== 'number') {
+        start = 0
+      }
+      
+      if (start + search.length > this.length) {
+        return false
+      } else {
+        return this.indexOf(search, start) !== -1
+      }
+    }
+  })
+}
 /* eslint-enable */