Hardhat prettierrc file using tabs

[damianmarti]

The prettierrc file in the hardhat package is using tabs for indentation (useTabs: true).

From the solidity style guide:

Indentation
Use 4 spaces per indentation level.

Tabs or Spaces
Spaces are the preferred indentation method.

Mixing tabs and spaces should be avoided.

Should we keep using tabs or should we move to spaces?

[damianmarti]

Changed at #994