Update README.md

Author: sf-jeff-lim

README.md

@@ -330,7 +330,7 @@ Incoming calls are received through the application's persistent internal server
 
 There are two types of event handlers the SDK provides for a client app to respond to various events: a device-specific listener and a call-specific listener.
 
-#### - Device-specific Listener
+#### - Device-specific listener
 
 Register a device-specific event handler using the `SendBirdCall.addListener()` method. It is recommended to add the event handler during initialization because it is a prerequisite for detecting an `onRinging()` event. The code below shows the way device-wide events such as incoming calls are handled once device-specific event is added. 
 
@@ -360,7 +360,7 @@ SendBirdCall.addListener(UNIQUE_HANDLER_ID, {
 |onAudioOutputDeviceChanged | Audio output devices have changed. |
 |onVideoInputDeviceChanged | Video input devices have changed. |
 
-#### - Call-specific Listener
+#### - Call-specific listener
 
 Register a call-specific event handler by attaching an event handler function directly to the properties of the call object. Responding to call-specific events such as establishing a successful call connection is then handled as shown below.