fix jslint errors

src/jio.storage/davstorage.js

@@ -181,7 +181,7 @@
    */
   var ajax = {
     "none": function (method, type, url, data) {
-      var headers;
+      var headers = {};
       if (method === "PROPFIND") {
         headers.Depth = "1";
       }

test/jio.storage/davstorage.livetests.js

@@ -113,7 +113,7 @@
 
     function list2DocumentsTest(answer) {
       if (answer && answer.data && Array.isArray(answer.data.rows)) {
-        answer.data.rows.sort(function (a, b) {
+        answer.data.rows.sort(function (a) {
           return a.id === "b" ? 1 : 0;
         });
       }