Update URLs used in release notes

Some URLs used in release notes became outdated.  Make sure they point
to currently available resources.

doc/arm/notes-download.xml

@@ -12,7 +12,7 @@
 <section xml:id="relnotes_download"><info><title>Download</title></info>
   <para>
     The latest versions of BIND 9 software can always be found at
-    <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.isc.org/downloads/">http://www.isc.org/downloads/</link>.
+    <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.isc.org/download/">https://www.isc.org/download/</link>.
     There you will find additional information about each release,
     source code, and pre-compiled versions for Microsoft Windows
     operating systems.

doc/arm/notes-eol.xml

@@ -20,7 +20,7 @@
     For those needing long term support, the current Extended Support
     Version (ESV) is BIND 9.11, which will be supported until at
     least December 2021. See
-    <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.isc.org/downloads/software-support-policy/">https://www.isc.org/downloads/software-support-policy/</link>
+    <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://kb.isc.org/docs/aa-00896">https://kb.isc.org/docs/aa-00896</link>
     for details of ISC's software support policy.
   </para>
 </section>

doc/arm/notes-thankyou.xml

@@ -14,6 +14,6 @@
     Thank you to everyone who assisted us in making this release possible.
     If you would like to contribute to ISC to assist us in continuing to
     make quality open source software, please visit our donations page at
-    <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.isc.org/donate/">http://www.isc.org/donate/</link>.
+    <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.isc.org/donate/">https://www.isc.org/donate/</link>.
   </para>
 </section>