fixed bug when setting up the documentation callback

updated the demo notebbok

notebooks/HDFViewerDemo.ipynb

@@ -7,11 +7,11 @@
 %% Cell type:code id: tags:
 
 ``` python
 import h5py
 
-from hdfviewer.widgets.HDFViewer import HDFViewer, HDFViewerWidget
+from hdfviewer.widgets.HDFViewer import HDFViewerWidget
 from hdfviewer.widgets.PathSelector import PathSelector
 ```
 
 %% Cell type:code id: tags:
 

src/hdfviewer/widgets/HDFViewer.py

@@ -20,7 +20,7 @@ def HDFViewerWidget(hdf, startPath=None):
 
     button = widgets.Button(description="documentation", tooltip="open documentation for release {0}".format(hdfviewer.__release__))
 
-    button.on_click(HDFViewer.info)
+    button.on_click(lambda event : HDFViewer.info())
 
     vbox.children = [button,HDFViewer(hdf,startPath)]