library: rpc: return nonce in SetActivity function

There's currently no way to obtain that value, so it is returned here to help with tinkering with the RPC server in the Discord client.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

activity.go

@@ -62,9 +62,9 @@ type activityArgs struct {
 	Activity *Activity `json:"activity"`
 }
 
-func (d *Client) SetActivity(act *Activity) error {
+func (d *Client) SetActivity(act *Activity) (string, error) {
 	if err := d.activate(); err != nil {
-		return err
+		return "", err
 	}
 
 	nonce := uuid.New().String()
@@ -80,5 +80,5 @@ func (d *Client) SetActivity(act *Activity) error {
 				Nonce:   nonce,
 			},
 		})
-	return err
+	return nonce, err
 }