Documentation: git-svn: fix a grammatical error without awkwardness

Documentation: git-svn: fix a grammatical error without awkwardness

The way the sentence is currently written, there needs to be an "its",
but this leads to: "however the remote wildcard may be anywhere as long
as it's its own" which is awkward to read.

Instead, this patch fixes he grammar in a simpler way.

Signed-off-by: Wesley J. Landaker <wjl@icecavern.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>