Update version to 0.3.8 to deploy `in_series`

[bwhite-mdsol]

Can anyone do these steps

git tag -a v0.3.8 -m "Git tag 0.3.8"
git push origin --tags
mix hex.publish

or does it need to be a maintainer?

[Olshansk]

https://hexdocs.pm/mock/0.3.8