Fix vertical alignment of reader author block in meta line

The .reader__author inline-flex box is sized by the 22px avatar, but
inline boxes default to vertical-align: baseline. That baseline-anchored
the tall author box against the shorter meta text (separators, date,
reading time), leaving the avatar visually misaligned. Aligning the
author box to vertical-align: middle puts the avatar, name, and trailing
meta text on a common centerline.