Ensure we exit with a code at the end

[tmeasday]

I missed this bit from the old code:

chromatic-cli/bin-src/main.ts

Lines 59 to 60 in b3fbf71

	log.info('');
	process.exit(ctx.exitCode);

Not sure if the log is still necessary but this solves the immediate problem

[skitterm]

This looks good to me, restores the process.exit() that we've had for awhile. Seems we can wait on making improvements to that part.