audio: fix play in background

Set mix category to allow play ringtone when app is in background

Change-Id: I6e5d50b03981e185877dc99c6c916f16369b3aa6
diff --git a/Ring/Ring/Services/AudioService.swift b/Ring/Ring/Services/AudioService.swift
index c372d0b..7cf7058 100644
--- a/Ring/Ring/Services/AudioService.swift
+++ b/Ring/Ring/Services/AudioService.swift
@@ -56,9 +56,9 @@
     func startAVAudioSession() {
         do {
             if #available(iOS 10.0, *) {
-                try AVAudioSession.sharedInstance().setCategory(.playAndRecord, mode: .default, options: [AVAudioSession.CategoryOptions.allowBluetooth])
+                try AVAudioSession.sharedInstance().setCategory(.playAndRecord, mode: .default, options: [AVAudioSession.CategoryOptions.allowBluetooth, AVAudioSession.CategoryOptions.mixWithOthers])
             } else {
-                try AVAudioSession.sharedInstance().setCategory(.playAndRecord, options: [AVAudioSession.CategoryOptions.allowBluetooth])
+                try AVAudioSession.sharedInstance().setCategory(.playAndRecord, options: [AVAudioSession.CategoryOptions.allowBluetooth, AVAudioSession.CategoryOptions.mixWithOthers])
             }
             try AVAudioSession.sharedInstance().setActive(true)
         } catch {