Make mergehex executable. (#4290)

Previously, we used sudo and chmod to make mergehex executable in
our build script. This change attempts to set the executable bit
using git properties and remove the dependence on elevated
permissions.

bin/build-nrf52.sh

@@ -35,7 +35,6 @@ SRCHEX=.pio/build/$1/firmware.hex
 # if WM1110 target, merge hex with softdevice 7.3.0
 if (echo $1 | grep -q "wio-sdk-wm1110"); then
 	echo "Merging with softdevice"
-	sudo chmod +x ./bin/mergehex
 	bin/mergehex -m bin/s140_nrf52_7.3.0_softdevice.hex $SRCHEX -o .pio/build/$1/$basename.hex
 	SRCHEX=.pio/build/$1/$basename.hex
 	bin/uf2conv.py $SRCHEX -c -o $OUTDIR/$basename.uf2 -f 0xADA52840