instanceinfo: Fix soapbox detection

Soapbox answers with a JSON error message.

instanceinfo.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 # Print some basic info about fediverse instances.
 
-# Version: 2021-02-22_1
+# Version: 2022-05-25_1
 
 if [[ -z "${1}" ]]; then
     echo "usage: ${0} DOMAIN" >&2
@@ -186,7 +186,7 @@ function main()
     local mastoinfo="https://${instance}/api/v1/instance"
     local misskeyinfo="https://${instance}/api/meta"
 
-    if ${mycurl} -ILf -X POST "${misskeyinfo}" | grep -iq 'Content-Type: application/json'; then
+    if ${mycurl} -ILf -X POST "${misskeyinfo}" | grep -iq 'HTTP.*200'; then
         echo "Misskey API found."
         parse_misskey "${instance}" "${misskeyinfo}"
     elif ${mycurl} -ILf "${nodeinfo}" | grep -iq 'Content-Type: application/json' \