Kangaroo UART TX & RX lines need pull-up resistors

At least one Kangaroo board went into command line mode when the test button was pressed due to noise on the RX line when no device was connected. The board should have gone back to sleep in 5 seconds but was stuck in a busy loop waiting for a valid command to be entered with no way to exit command line mode.

A pull-up resistor will pull the line to the idle state by default.

A pull-up on the TX line isn't as necessary, but it may avoid noise characters being sent to a connected device in some circumstances, such as when the node is powered on.