bugfix for get_person_mentions(unread_only=...)

[feelixs]

When unread_only is given as a Python bool, fix error "Query deserialize error: provided string was not true or false"

[tjkessler]

@mike-fmh,

Interesting, I had assumed either the requests library or Lemmy itself would handle the type conversion. Nice catch, and an elegant solution. I'll merge, new version will be 0.3.3!

Travis