Add kCommandAcks to CapabilityType enum.

protocol/proto/spirc.proto

@@ -66,6 +66,7 @@ enum CapabilityType {
     kIsObservable = 0x7;
     kVolumeSteps = 0x8;
     kSupportedTypes = 0x9;
+    kCommandAcks = 0xa;
 }
 
 message Goodbye {