Documentation/bup-split.md: fix a parser error.
Documentation/bup-split.md: fix a parser error.

The version of pandoc that I use doesn't like quotation marks, so use single
quotes instead.

Signed-off-by: Avery Pennarun <e03ccfb89d416c4697ad6970ce86a92c1c28a78e@gmail.com>

jbaber/bup,mhoeher/bup,pombredanne/bup,tjanez/bup,jbaber/bup,jbaber/bup,apenwarr/bup,jbaber/bup,tjanez/bup,pombredanne/bup,mhoeher/bup,jbaber/bup,apenwarr/bup,tjanez/bup,ToxicFrog/bup,gevaerts/bup,pombredanne/bup,mhoeher/bup,pombredanne/bup,gevaerts/bup,ToxicFrog/bup,gevaerts/bup,gevaerts/bup,mhoeher/bup,pombredanne/bup,mhoeher/bup,pombredanne/bup,tjanez/bup,ToxicFrog/bup,ToxicFrog/bup,jbaber/bup,gevaerts/bup,apenwarr/bup,tjanez/bup,tjanez/bup,apenwarr/bup,mhoeher/bup,ToxicFrog/bup