set to 4.2
add md5sum
Merge branch 'master' of https://github.com/qq978304139/rk_upgrade_tools

Conflicts:
	rockdev/.gitignore
	rockdev/mkupdate.sh
Merge branch 'master' into RK3188_4.2
Merge branch 'RK3188_4.2' of https://github.com/qq978304139/rk_upgrade_tools into RK3188_4.4

Conflicts:
	rockdev/parameter