Moves existing devDependencies to dependencies

[scinos]

Changes proposed in this Pull Request

• Moves devDependencies into dependencies. This is a pre-requisite to moving to yarn.

Testing instructions

Checkout the branch and do a diff of package-lock.json against master. Use grep to remove irrelevant bits (lots of changes in dev: true and extra commas for integrity). For example:

git diff -U0 master.. -- package-lock.json | grep -v '"dev": true' | grep -v '@@ '| grep  -v '"integrity"' | grep -v '"resolved"'

The result should show any effective change in the dependency tree. You'll see there are very few changes, all caused by applying different hoisting rules to wp-prettier@1.19.1 and is-number

[matticbot]

Test live: https://calypso.live/?branch=update/devdeps-to-deps

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.