[FIX] Web: view_pivot.js: download table with one measure

The headers array contains 2 sub-arrays, whatever the number of
measures. The test on nbr_measures was thus incorrect and produced an
error when downloading a table with a single measure.

Also fix the typo in dow(n)load_table function name.

addons/web/static/src/js/view_pivot.js

@@ -71,7 +71,7 @@ instance.web.PivotView = instance.web.View.extend({
                     self.sidebar.appendTo(self.$sidebar);
                     self.sidebar.add_items('other', [{
                         label: _t("Download xls"),
-                        callback: self.dowload_table.bind(self)
+                        callback: self.download_table.bind(self)
                     }]);
                 }
             });
@@ -199,7 +199,7 @@ instance.web.PivotView = instance.web.View.extend({
             return this.toggle_measure(field);
         }
         if ($target.hasClass('oe-pivot-download')) {
-            return this.dowload_table();
+            return this.download_table();
         }
     },
     on_open_header_click: function (event) {
@@ -731,7 +731,7 @@ instance.web.PivotView = instance.web.View.extend({
             this.load_data().then(this.display_table.bind(this));
         }
     },
-    dowload_table: function () {
+    download_table: function () {
         openerp.web.blockUI();
         var nbr_measures = this.active_measures.length,
             headers = this.compute_headers(),
@@ -754,7 +754,7 @@ instance.web.PivotView = instance.web.View.extend({
             }
         }
         var table = {
-            headers: nbr_measures > 1 ? _.initial(headers) : headers,
+            headers: _.initial(headers),
             measure_row: measure_row,
             rows: rows,
             nbr_measures: nbr_measures,