Linux client UnlockFolders paper key entry field does not receive keyboard input

#### Issue description
When attempting to enter a paper key into the client UI UnlockFolders window, none of my keyboard input is entered into the entry field. I can enter the paper key just fine if I initiate a rekey via the command line with `keybase rekey paper`.

Devices involved:
device_a : macOS 10.13.4 - keybase v 2.0.0-201806044163023+f899a761a7
device_b : Android 8.1.0 - keybase v 1.0.49-21080605022941+da5061f5ff
device_c : Pop!_OS (Ubuntu) 18.04 - keybase v 2.1.0-20180615162035+8625b772b1

#### Steps to reproduce the issue

1. add `device_c` using mobile app on `device_b`
2. create new paper key on `device_c` when prompted by client UI
3. rekey event is triggered
4. client UI opens UnlockFolders prompt for rekey using another connected client or paper key
5. click `Use a paper key instead`
6. Type

#### What's the expected result?

- Field populates with the characters I type or paste in

#### What's the actual result?

- Nothing gets entered into the field. Attempting to proceed results in an error 204 - not enough words entered for a paper key

#### Additional details / screenshot

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Start by reproducing the UnlockFolders paper-key prompt on the Linux client, then compare it with the working `keybase rekey paper` command. Done means the field accepts typed or pasted paper-key words and proceeding no longer reports error 204.

Written by the indexing model from the issue text.