add this function to your .zshrc or .bashrc file to update chromium to the latest nightly with a command.

updatechromium.sh

updatechromium () {
	Platform='unknown'
	platform='unknown'
	unamestr=`uname`
	case "$unamestr" in
		('Darwin') Platform="Mac"
			platform="mac"  ;;
		('Linux') Platform="Linux"
			platform="linux"  ;;
		(*) if [[ $# = 2 ]]
			then
				Platform=$(echo "$2" | sed -e "s/\([^\.]\+\)/\u\1/g")
				platform=$(echo "$2" | tr '[A-Z]' '[a-z]')
			elif [[ $# = 1 ]]
			then
				Platform=$(echo "$1" | sed -e "s/\([^\.]\+\)/\u\1/g")
				platform=$(echo "$1" | tr '[A-Z]' '[a-z]')
			fi ;;
	esac
	echo "$unamestr :: $Platform : $platform"
	echo
	BASEDIR=http://commondatastorage.googleapis.com/chromium-browser-continuous/$Platform
	cd ~/$1
	echo "Downloading number of latest revision"
	REVNUM=`curl -# $BASEDIR/LAST_CHANGE`
	echo "Found latest revision number $REVNUM, starting download"
	curl $BASEDIR/$REVNUM/chrome-$platform.zip > $REVNUM.zip
	echo "Unzipping..."
	unzip $REVNUM.zip 2>&1 > /dev/null
	echo "Done."
	rm -rf /Applications/Chromium.app
	mv chrome-mac/Chromium.app /Applications/Chromium.app
	rm -rf chrome-mac
	rm -rf $REVNUM.zip
	echo "Moving to Applications directory..."
	echo "Done, update successful"
}

Add that to your bashrc or zshrc and then just call the function

> updatechromium

(Note: I can't remember where I stole the parts of this from, but I'm just pasting it here cause some peeps asked for it. I had to update some URLs and paths to make it work for me. So apologies if you wrote it. Claim it here!)