push doc: add spacing between two words

Fix a formatting error introduced in my recently landed
fe802bd21e ("push doc: correct lies about how push refspecs work",
2018-08-31).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-push.txt

@@ -110,7 +110,7 @@ can be overridden by adding an the optional leading `+` to a refspec
 is that no amount of forcing will make the `refs/heads/*` namespace
 accept a non-commit object. Hooks and configuration can also override
 or amend these rules, see e.g. `receive.denyNonFastForwards` in
-linkgit:git-config[1] and`pre-receive` and `update` in
+linkgit:git-config[1] and `pre-receive` and `update` in
 linkgit:githooks[5].
 +
 Pushing an empty <src> allows you to delete the <dst> ref from the