tf-a-lts-docs-watcher.sh: Support tags with slash in name

E.g. sandbox/lts-v2.10.3

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I370aec7bca5ca7161b148309f1fe283ec3d52d92
diff --git a/scripts/tf-a-lts-docs-watcher.sh b/scripts/tf-a-lts-docs-watcher.sh
index ae50e98..dc35b97 100755
--- a/scripts/tf-a-lts-docs-watcher.sh
+++ b/scripts/tf-a-lts-docs-watcher.sh
@@ -14,7 +14,10 @@
 new_tag=""
 refname=${GERRIT_REFNAME##*/}
 lts_branch=${refname}
-echo ${GERRIT_REFNAME} | grep -q "refs\/tags\/" && lts_branch=${refname%.*} && new_tag=${refname}
+if echo ${GERRIT_REFNAME} | grep -q "refs/tags/"; then
+    new_tag=${GERRIT_REFNAME#refs/tags/}
+    lts_branch=${refname%.*}
+fi
 
 function activate_version() {
     version=$1