Python package name

A package name with dashes in invalid in Python!

Author: zerline

cookiecutter.json

@@ -3,7 +3,7 @@
 	"author_email": "",
 	"github_project_name": "jupyter-widget-example",
 	"github_organization_name": "",
-	"python_package_name": "{{ cookiecutter.github_project_name }}",
+	"python_package_name": "jupyter_widget_example",
 	"npm_package_name": "{{ cookiecutter.github_project_name }}",
 	"npm_package_version": "0.1.0",
 	"project_short_description": "A Custom Jupyter Widget Library"