Fix GitbookIO#641: fix progress order in json format

Author: SamyPesse

lib/utils/navigation.js

@@ -57,6 +57,7 @@ function navigation(summary, files) {
 
 
         return [current.path, {
+            index: i,
             title: current.title,
             prev: prev,
             next: next,

lib/utils/progress.js

@@ -7,10 +7,18 @@ var calculProgress = function(navigation, current) {
     var done = true;
 
     var chapters = _.chain(navigation)
+
+    // Transform as array
     .map(function(nav, path) {
         nav.path = path;
         return nav;
     })
+
+    // Sort entries
+    .sortBy(function(nav) {
+        return nav.index;
+    })
+
     .map(function(nav, i) {
         // Calcul percent
         nav.percent = (i * 100) / Math.max((n - 1), 1);