fix symbols for \rightarrowtail and \leftarrowtail in math.satyh

[coord-e]

I found that \rightarrowtail and \leftarrowtail seem to be defined incorrectly in math.satyh.
This PR corrects them.

before:

after:

@require: standalone
@require: code
@require: math
@require: itemize

standalone '<
  +listing {
    * \code(`\rightarrowtail`);: ${\rightarrowtail}
    * \code(`\leftarrowtail`);: ${\leftarrowtail}
  }
>

[gfngfn]

I didn’t notice that. Thank you for fixing!