Update dns_bunny.sh

`i` should start with `1`.
In dns alias mode, the fulldomain doesn't have a `_acme-challenge` prefix.

dnsapi/dns_bunny.sh

@@ -198,9 +198,7 @@ _get_base_domain() {
     fi
     _debug2 domain_list "$domain_list"
 
-    ## for each shortening of our $fulldomain, check if it exists in the $domain_list
-    ## can never start on 1 (aka whole $fulldomain) as $fulldomain starts with "_acme-challenge"
-    i=2
+    i=1
     while [ $i -gt 0 ]; do
       ## get next longest domain
       _domain=$(printf "%s" "$fulldomain" | cut -d . -f "$i"-"$MAX_DOM")