Switch linting to ESLint and Prettier (#191)

* Switch linting to ESLint and Prettier
* Clean up config
* Prettier fixes

lib/uniqueid.js

@@ -1,8 +1,8 @@
 module.exports = (function() {
-  var counter = 0
+  var counter = 0;
   return function() {
-    var id = ("pjax" + (new Date().getTime())) + "_" + counter
-    counter++
-    return id
-  }
-})()
+    var id = "pjax" + new Date().getTime() + "_" + counter;
+    counter++;
+    return id;
+  };
+})();