fix(ci): Don't update webdriver in pretest
Doing this automatically means we can't pin the version of webdriver
that we use in CI. Instead, we run update in the circle config.
chore(release): version bump to 6.0.0 and update the changelog
Since the current changelog between the 6.0.0-beta and the 6.0.0 release
is minor, updated the changelog by removing the -beta.