Direct references are considered unpinned

[Harmon758]

Pip has supported direct references since version 19.1.
Pyup seems to ignore them and consider the requirement unpinned, e.g. Harmon758/Harmonbot#2495 and Harmon758/Harmonbot#2496, due to Harmon758/Harmonbot@35b03d9 (both also show "unpinned" as the status in the repo dashboard).
It should probably ignore requirements that use direct references instead, in the same way that requirements installed directly from a URL using the egg suffix are ignored.