#390: correct column name is outbound_sip_proxy (#391)

db/upgrade-jambonz-db.js

@@ -209,7 +209,7 @@ const sql = {
     'ALTER TABLE google_custom_voices ADD COLUMN voice_cloning_key MEDIUMTEXT',
     'ALTER TABLE google_custom_voices ADD COLUMN use_voice_cloning_key BOOLEAN DEFAULT false',
     'ALTER TABLE voip_carriers ADD COLUMN dtmf_type ENUM(\'rfc2833\',\'tones\',\'info\') NOT NULL DEFAULT \'rfc2833\'',
-    'ALTER TABLE voip_carriers ADD COLUMN sip_proxy VARCHAR(255)',
+    'ALTER TABLE voip_carriers ADD COLUMN outbound_sip_proxy VARCHAR(255)',
   ]
 };