Can't use backspace while speaking because it stops the app.

**Describe the bug**
  I only have one trigger command sp option space so I'm thinking I should only use that specific trigger to stop the app but currently when I type backspace because of how it adds an extra space for me (see #158) it completely stops the app and quits the app and transcribes the thing.

**To Reproduce**
Steps to reproduce the behavior:
1.   Use option space as keyboard shortcut and start talking.
2.   Now start talking and press backspace or delete

**Expected behavior**
  The backspace should work as is similarly space should work and give space as well.

**Desktop (please complete the following information):**
- 0.6.9

Reproduce the issue in the macOS app using Option-Space, then inspect the keyboard shortcut and text-input handling described by the reproduction steps. Confirm that Backspace and Delete no longer stop or quit the app, while Space still inserts a space and transcription continues as expected.

Written by the indexing model from the issue text.