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
Greg Ward, author of the original bfiles extension
Na'Tosha Bard of Unity Technologies
Fog Creek Software
Special thanks to the University of Toronto and the UCOSP program