Signify highlights are incorrect

[pbnj]

Problem

I'm not sure why Signify highlights are incorrectly set to LineNr here, but GitGutter highlights are correctly set to their respective colors.

Proposed Solution

Signify highlights can either be linked to DiffAdd, DiffDelete, and DiffChanged (as original defined in Signify plugin here) or they can be set in this colorscheme to their respective colors, just as GitGutter signs are set, via:

call s:h("SignifySignAdd", {"fg": s:green, "bg": s:bg_subtle})
call s:h("SignifySignDelete", {"fg": s:red, "bg": s:bg_subtle})
call s:h("SignifySignChange", {"fg": s:yellow, "bg": s:bg_subtle})
call s:h("SignifyLineDeleteFirstLine", {"fg": s:red, "bg": s:bg_subtle})

Let me know which solution you prefer to implement and I can send in a PR.