beautifygraph: change the current commit symbol
The existing "circle with vertical fill" character renders as full width in
many terminals making the beautified symbols have uneven size. Additionally,
the proposed "fisheye" character is the logic 'active' version of the current
merge symbol, "bullseye."
Differential Revision: https://phab.mercurial-scm.org/D9678
edition = "2018"
max_width = 79
wrap_comments = true
error_on_line_overflow = true