Upgrade the mix_audit dependancy

[sigu]

Is your feature request related to a problem? Please describe.
There are existing deprecation warnings with the mix_audit library that have now been fixed in version 2.1.4

Describe the solution you'd like
Improve developer experience by removing warnings and also making upgrade path easier in the future

Describe alternatives you've considered
Wait for some time to find out if there are known bugs introduced with the new release

Express the feature either with a change to resource syntax, or with a change to the resource interface

This is only chaniging on the dev enviroment, the mix file and mix lock files

Additional context

Changes were introduced in this PR: mirego/mix_audit#28, no breaking changes expected from this update