docs(changelog): fix version tag links

The Standard Version tool will not recognize a release header as a
release header without the minor version, and will overwrite them when
generating the next release changelog.

Additionally, it will not generate a link to the tag diff unless a tag
of the form `vX.Y.Z` exists. We ought to generate tags with this version
format in the future to ensure the diff links are generated.

Change-Id: I7864ab7a5822f83ddb7a7917208d2d029ae34729
Signed-off-by: Chris Kay <chris.kay@arm.com>
diff --git a/.versionrc.js b/.versionrc.js
index 5005c73..fa6a26f 100644
--- a/.versionrc.js
+++ b/.versionrc.js
@@ -64,7 +64,7 @@
     "preset": {
         "name": "tf-a",
         "commitUrlFormat": "https://review.trustedfirmware.org/plugins/gitiles/TF-A/trusted-firmware-a/+/{{hash}}",
-        "compareUrlFormat": "https://review.trustedfirmware.org/plugins/gitiles/TF-A/trusted-firmware-a/+/{{previousTag}}..{{currentTag}}",
+        "compareUrlFormat": "https://review.trustedfirmware.org/plugins/gitiles/TF-A/trusted-firmware-a/+/refs/tags/{{previousTag}}..refs/tags/{{currentTag}}",
         "userUrlFormat": "https://github.com/{{user}}",
 
         "types": types,