Resolve build issue when adding `CeloProvider` (cont of #761)

[tamagosante]

#761
#761 (comment)

Copy paste:

Celo-Tools

https://www.npmjs.com/package/@celo-tools/celo-ethers-wrapper
CeloProvider is a wrapper that enables Ethersjs to work with the Celo network. Specific for launch it might solve the getBlock workaround, since Celo is not supporting gasLimit.
It is implemented to create the readOnlyProvider in EthereumService.

Quick test to implement Celo-Tools in prime-launch ended with an error:

this.readOnlyProvider = new CeloProvider(...);