print: impvove Lit case in wordPart()
print: impvove Lit case in wordPart()

It's hit very often.

name      old time/op    new time/op    delta
Fprint-4    6.81µs ± 0%    6.64µs ± 1%  -2.61%          (p=0.010 n=4+6)

mvdan/sh,mvdan/sh,mvdan/sh,mvdan/sh