CSS ordering conflict with DatePicker month/year choosers

[spefley]

Environment

• Package version(s):
  "@blueprintjs/core": "^3.6.0",
  "@blueprintjs/datetime": "^3.2.0",
  "@blueprintjs/select": "^3.2.0",
• Browser and OS versions:
  Chrome 68.0.3440.106 (Official Build)
  Mac OS High Sierra 10.13.4

I checked and the css that's overriding the datetime select styles here comes from the core package

Order of css imported: 1. core 2. datetime 3. select

Order of css imported: 1. core 2. select 3. datetime

[spefley]

@giladgray this is the result of a standing bug in mini-css-extract-plugin that means css isn't necessarily ordered (see: webpack-contrib/mini-css-extract-plugin#188). This doesn't happen in bp because it's still on webpack 3 with extract-text-webpack-plugin (though that also has issues w/ ordering, see: webpack-contrib/extract-text-webpack-plugin#200).