sysutils/bkt: update to 0.7.0

What's Changed
- stdout/stderr are now streamed as the subprocess is executing, rather than
  output only once the subprocess completes (#43).
- NotFound errors during cleanup are now ignored (#42).
- Improved error handling for malformed executables (#37).

API Changes
- New methods Bkt::retrieve_streaming and Bkt::refresh_streaming have been
  added for library users that want to stream output, however these methods
  are subject to change and should be treated as experimental.

(pin)