update gpg keyserver as old one deprecated

Signed-off-by: Rui Yang <ruiya@vmware.com>

Author: Rui Yang

README.md

@@ -97,7 +97,7 @@ Tracks the commits in a [git](http://git-scm.com/) repository.
   `gpg_keyserver`. The ids can be short id, long id or fingerprint.
 
 * `gpg_keyserver`: *Optional.* GPG keyserver to download the public keys from.
-  Defaults to `hkp:///keys.gnupg.net/`.
+  Defaults to `hkp://keyserver.ubuntu.com/`.
 
 * `git_crypt_key`: *Optional.* Base64 encoded
   [git-crypt](https://github.com/AGWA/git-crypt) key. Setting this will

assets/in

@@ -46,7 +46,7 @@ commit_verification_keys=$(jq -r '(.source.commit_verification_keys // [])[]' <<
 tag_filter=$(jq -r '.source.tag_filter // ""' <<< "$payload")
 tag_regex=$(jq -r '.source.tag_regex // ""' <<< "$payload")
 fetch_tags=$(jq -r '.params.fetch_tags' <<< "$payload")
-gpg_keyserver=$(jq -r '.source.gpg_keyserver // "hkp://ipv4.pool.sks-keyservers.net/"' <<< "$payload")
+gpg_keyserver=$(jq -r '.source.gpg_keyserver // "hkp://keyserver.ubuntu.com/"' <<< "$payload")
 disable_git_lfs=$(jq -r '(.params.disable_git_lfs // false)' <<< "$payload")
 clean_tags=$(jq -r '(.params.clean_tags // false)' <<< "$payload")
 short_ref_format=$(jq -r '(.params.short_ref_format // "%s")' <<< "$payload")