Fix typos:   `overriden` -> `overridden`   `whene` -> `when`   `focussed` -> `focused`   `themself` -> `themselves`   `opperating` -> `operating`
Fix typos:
  `overriden` -> `overridden`
  `whene` -> `when`
  `focussed` -> `focused`
  `themself` -> `themselves`
  `opperating` -> `operating`

jonathanslenders/python-prompt-toolkit