Dismiss uport modal throws an error

[Akaryatrh]

Describe the bug
If user dismisses uport modalbox containing QRCode, an error is thrown on console:

Uncaught (in promise) TypeError: Failed to execute 'removeChild' on 'Node': parameter 1 is not of type 'Node'. at close (index.js:50)

To Reproduce
Steps to reproduce the behavior:

1. Install uport-connect npm package v1.1.1
2. Call method uport.requestDisclosure() on your code
3. Wait for modalbox to pop-in, and click on close icon on top-right corner of modalbox
4. See error on console

Desktop (please complete the following information):

• OS: OSX
• Browser: Chrome
• Version: 71.0.3578.98

Additional context
Error seems to come from uPort transport, here: https://github.com/uport-project/uport-transports/blob/62d0275946ee49abdf952fa4855278801925812c/src/transport/ui/index.js#L30