move inst-ui from 'dev-dependencies' to prod
move inst-ui from 'dev-dependencies' to prod

fixes: CNVS-30799

...since it is not just needed for our build
tooling, it is actually needed in the actual app
because common.scss @import ../../../node_modules/instructure-ui/dist/instructure-ui
directly. so without having this in the prod
dependencies, it will blow up when someone
tries to preview in the theme editor and at deploy
time when we run brand_configs

test plan:

run these terminal commands:
* rm -rf node_modules
* npm install --production
* node_modules/.bin/brandable_css
those should work.

now open theme editor
make a change
hit preview
it should work

Change-Id: I87e9896e668d16b653e868bd202a807c204f2f95
Reviewed-on: https://gerrit.instructure.com/87027
Reviewed-by: Neil Gupta <cc4fec8a34766005dd45d48be045c08d736c11ed@instructure.com>
Tested-by: Jenkins
Product-Review: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>
QA-Review: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>

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