Change MaxUint32 to MaxInt32
Change MaxUint32 to MaxInt32

This change was implemented to address the following message, reported by the raspberry pi golang compiler (v1.12):

/home/pi/go/pkg/mod/github.com/mum4k/termdash@v0.9.0/widgets/text/scroll.go:119:29: constant 4294967295 overflows int

mum4k/termdash,mum4k/termdash