Trailing register/define key mis-documented

[dbranford]

The manual gives acro/trailing/define as the key to add additional trailing characters but this is undefined and the source uses acro/trailing/register instead

acro/doc/acro-manual.tex

Line 1587 in 9a56e41

trailing/define = . {dot} ,

acro/code/acro.tools.code.tex

Line 486 in d2479bb

register .code:n = \acro_trailing_token_register:Nn #1 ,