since 'echo' behaves differently on freebsd and debian with respect to backslashes.

This led to the following error while trying to compile the dtx file on freebsd:
(./automultiplechoice.sty
AMC version: 2018/05/02 v1.4.0\\string\nobreakspace {}beta1
! Undefined control sequence.
\\  ->\let \reserved@e
                        \relax \let \reserved@f \relax \@ifstar {\let
\reserv...
l.30 ...sPackage{automultiplechoice}[\AMC@VERSION]

!  ==> Fatal error occurred, no output PDF file produced!
Transcript written on automultiplechoice.log.