Fix for "bossac: extra arguments found"

I am on Windows 10 (unfortunately!). The command:

…bossac.exe -i -d --port=COMX -U false -e -w -b …bin -R

fails for me, it should be changed to:

…bossac.exe -i -d --port=COMX -U=false -e -w -b …bin -R

(-U false >> -U=false)

to solve the problem in my case. This may not happen for everyone, but it would be more explicit to do that.

Thanks for the grate job!