add 'mapbox' to layout attributes

Author: etpinard

src/plots/layout_attributes.js

@@ -187,6 +187,7 @@ module.exports = {
         'annotations': 'Annotations',
         'shapes': 'Shapes',
         'images': 'Images',
-        'ternary': 'ternary'
+        'ternary': 'ternary',
+        'mapbox': 'mapbox'
     }
 };

test/jasmine/tests/plotschema_test.js

@@ -91,7 +91,7 @@ describe('plot schema', function() {
 
     it('all subplot objects should contain _isSubplotObj', function() {
         var IS_SUBPLOT_OBJ = '_isSubplotObj',
-            astrs = ['xaxis', 'yaxis', 'scene', 'geo', 'ternary'],
+            astrs = ['xaxis', 'yaxis', 'scene', 'geo', 'ternary', 'mapbox'],
             list = [];
 
         // check if the subplot objects have '_isSubplotObj'