doc: Fix formatting in rest-api-changes.txt

Add a missing space before the '+' symbol. The missing space was causing
the '+' to show up in the rendered web page instead of introducing a
line break.

Release-Notes: Improve docs
Change-Id: I445ac633cd2bdd2f99dfa3afceff8b5312f5eda9

Documentation/rest-api-changes.txt

diff --git a/Documentation/rest-api-changes.txt b/Documentation/rest-api-changes.txt
index e2e3f71..f3dc24a 100644
--- a/Documentation/rest-api-changes.txt
+++ b/Documentation/rest-api-changes.txt
@@ -9493,7 +9493,7 @@
 Notify handling that defines to whom email notifications should be sent after
 the change is submitted. +
 Allowed values are `NONE`, `OWNER`, `OWNER_REVIEWERS` and `ALL`. +
-If not set, the default is `ALL`.+
+If not set, the default is `ALL`. +
 Ignored if a post approval diff is present (i.e. if the change is submitted
 with copied approvals), because in this case everyone should be informed
 about the non-reviewed diff which has been applied after the change has been