getGains returns the current gains
 
    This method returns the latest received gains. It returns
    immediately and may return the same result more than once.
    Note that gain structs get populated by lookup requests,
    which usually get requested at a lower rate than feedback.
    If gain info is not available, this method will return
    empty ([]).
 
    If gains return empty or do not update as expected, confirm
    that the lookup polling rate is larger than zero.
 
    Example
       % Display the lookup polling rate
       HebiLookup
 
    Example
       % Double position kp gains on all modules
       gains = group.getGains()
       gains.positionKp = gains.positionKp * 2;
       group.send('gains', gains);