Add back step attribute for play widget.

Author: jasongrout

ipywidgets/widgets/widget_int.py

@@ -220,6 +220,7 @@ def _validate_value(self, proposal):
 @register
 class Play(_BoundedInt):
     interval = CInt(100).tag(sync=True)
+    step = CInt(1, help="Increment step").tag(sync=True)
 
     _view_name = Unicode('PlayView').tag(sync=True)
     _model_name = Unicode('PlayModel').tag(sync=True)

jupyter-js-widgets/src/widget_int.ts

@@ -709,7 +709,8 @@ class PlayModel extends BoundedIntModel {
             _model_name: 'PlayModel',
             _view_name: 'PlayView',
             _playing: false,
-            interval: 100
+            interval: 100,
+            step: 1,
         });
     }
     initialize(attributes, options) {