change key to snake case

Author: djih

src/amplitude-client.js

@@ -897,7 +897,7 @@ AmplitudeClient.prototype._logEvent = function _logEvent(eventType, eventPropert
 
     userProperties = userProperties || {};
     var trackingOptions = _generateApiPropertiesTrackingConfig(this);
-    trackingOptions = Object.keys(trackingOptions).length > 0 ? {trackingOptions: trackingOptions} : {};
+    trackingOptions = Object.keys(trackingOptions).length > 0 ? {tracking_options: trackingOptions} : {};
     apiProperties = merge(trackingOptions, (apiProperties || {}));
     eventProperties = eventProperties || {};
     groups = groups || {};

test/amplitude-client.js

@@ -1182,7 +1182,7 @@ describe('setVersionName', function() {
 
       // verify country is not sent since it matches the default value of true
       assert.deepEqual(events[0].api_properties, {
-        trackingOptions: {
+        tracking_options: {
           city: false,
           ip_address: false,
         }