Remove trailing slash after joining blueprint url_prefix and path
Remove trailing slash after joining blueprint url_prefix and path

Now blueprints can have root routes and, when registered on some path,
will not have trailing slash.

Example:
  ...
  @bp.route('/')
  def viewfn():
    ...

  ...
  app.register_blueprint(bp, url_prefix='/user')

Before this fix, this scenario results on error since the resulting
path is "/user/". After this fix, the resulting path is "/user".

awslabs/chalice