TypeScript zIndex definitions not updated with beta26 changes

[radicand]

• I have searched the issues of this repository and believe that this is not a duplicate.

Expected Behavior

When using the latest beta26 under TypeScript, I expect to be able to leverage the changes to zIndex, namely theme.zIndex.drawer.

Current Behavior

The TypeScript typings were not updated with the changes, and reference removed keys as well as lacking the newer (e.g., drawer, etc) keys.

Steps to Reproduce (for bugs)

1. Look at: https://github.com/mui-org/material-ui/blob/bd42549ee464bce03743f7ee18964066f9d3907d/src/styles/zIndex.js
2. Then look at the type definition: https://github.com/mui-org/material-ui/blob/bd42549ee464bce03743f7ee18964066f9d3907d/src/styles/zIndex.d.ts
3. Note the differences in keys defined for zIndex (also noted in the Changelog: https://github.com/mui-org/material-ui/releases/tag/v1.0.0-beta.26)

Context

I was previously using theme.zIndex.navDrawer, and on upgrading to beta26 noticed that I had styling issues -- further investigation revealed the zIndex wasn't being set at all, but this wasn't caught by the TypeScript compiler (because the types hadn't been updated).

Your Environment

TypeScript 2.6.2, NodeJS 8.9.1, OSX High Sierra

Tech	Version
Material-UI	1.0.0-beta26
React	16.2.0
browser	Chrome 63.0.3239.84 (Official Build) (64-bit) OSX

[oliviertassinari]

My bad. I should have updated the definitions. Do you want to take care of it? :)

[radicand]

Sure, I'll send a pull request shortly.