Ensure there's only one command line
    
    The surrounding formatting code is not capable of treating multi-line
    properly here, so this was not assumed.
    
    While we could support multi-line nag commands, due to nature of merging
    in inigrep and Saturnin, it would only bring risk.  Also it would not be
    consistent with how other fields like timeout or color are treated,
    which would be confusing from user POV.