Move jest to dev dependencies

[kerimhudson]

Describe the bug
A clear and concise description of what the bug is.

Jest is installed as a dependency, not a dev dependency. This caused us some issues regarding module resolutions (specifically with Prisma and Decimal.js), throwing typescript errors due to the differences between latest version of Decimal.js (10.3.1) and the version used by Jest (10.2.0).

To Reproduce

Please provide a codesandbox of your issue or I will not be able to diagnose and fix it.

Install Decimal.js and this package in the same repo. Decimal.js typings will be that of the version in jest (10.2.0), and not the latest (10.3.1).