Using an Icon in a Header ignores Icon size prop

[adamvanaken]

Bug Report

Steps

Using an Icon in a Header ignores the Icon size prop.

I understand that I could easily override the styling, but I don't want to potentially break or miss out on future styling updates by doing so.

Expected Result

I would expect to be able to size Icons inside Headers.

Actual Result

The .ui.header>.icon style overrides the font-size that, as an example, the i.small.icon style sets.

Version

2.0.4

Testcase

https://codesandbox.io/s/semantic-ui-react-forked-38ue7