Bug#976301: Fix invalid `changelog` format example

[Anatoli Babenia <anatoli@rainforce.org>]

Package: debian-policy
Control: tag -1 + patch

Hello,

I am seeking seconds for the following patch:

diff --git a/policy/ch-source.rst b/policy/ch-source.rst
index edae8c1..1265c5e 100644
--- a/policy/ch-source.rst
+++ b/policy/ch-source.rst
@@ -126,7 +126,7 @@ That format is a series of entries like this:
      [blank line(s), included in output of dpkg-parsechangelog]
      * even more change details
      [optional blank line(s), stripped]
    [----]{+[space]--+} maintainer name <email address>[two [-spaces]
date-]{+spaces]date+}

``package`` and ``version`` are the source package name and version
number.