typo in documentation

[zimmermann6]

Component: documentation

Issue created by migration from https://trac.sagemath.org/ticket/1140

[mwhansen]

comment:1

Attachment: 7210.patch.gz

[sagetrac-cwitty]

comment:3

Looks good to me.

[sagetrac-mabshoff]

comment:4

Merged in 2.8.13.alpha0.