Fix badge formatting in README.md

Author: Carreau

python/widgetsnbextension/README.md

@@ -1,6 +1,6 @@
 # Jupyter Widgets for Jupyter Notebook
 
-![Version](https://img.shields.io/pypi/v/ipywidgets.svg?logo=pypi)](https://pypi.python.org/pypi/ipywidgets)
+[![Version](https://img.shields.io/pypi/v/ipywidgets.svg?logo=pypi)](https://pypi.python.org/pypi/ipywidgets)
 
 This package makes Jupyter widgets available in the classic Jupyter Notebook. This package provides the necessary JavaScript controls in the Jupyter Notebook that communicate with the widget objects in the kernel.