allow boostAudioSignal from updateCall (#523)

lib/routes/api/accounts.js

@@ -298,7 +298,8 @@ function validateUpdateCall(opts) {
     'tag',
     'dtmf',
     'conferenceParticipantAction',
-    'dub'
+    'dub',
+    'boostAudioSignal'
   ]
     .reduce((acc, prop) => (opts[prop] ? ++acc : acc), 0);