Fix typo in stack effect docs
Fix typo in stack effect docs

mcandre/factor,mcandre/factor,erg/factor,ceninan/factor,cataska/factor,erg/factor,mcandre/factor,erg/factor,mcandre/factor,kingcons/factor,mcandre/factor,mcandre/factor,cataska/factor,ceninan/factor,ceninan/factor,cataska/factor,erg/factor,erg/factor,kingcons/factor,ceninan/factor,mcandre/factor,erg/factor,kingcons/factor,cataska/factor,erg/factor,kingcons/factor