Update deprecated packages

[ChristopherDedominici]

Update deprecated packages:

• ethers
• mocha

Remove deprecated packages:

• request
• request-promise-native

[cgewecke]

@ChristopherDedominici Sorry for a pre-emptive review ... I think this might be a bit tricky. The package is super old.

Maybe PR could be split into a few pieces

• make changes for newer ethers
• do something about request
• bump mocha

I'm happy to do the first two, would you like to just make this one a mocha bump?

[frangio]

See #295

[cgewecke]

@ChristopherDedominici If you are continuing with this it will be necessary to rebase against master to get the tests running. The repo was not working with more recent versions of Node.

@frangio Updated mocha in #295 (merged)

[ChristopherDedominici]

@cgewecke I split this PR into smaller ones:

• bump ethers version: Bump ethers version #296
• request: it seems that the request package is not used, it should be removed: Remove unused request package #297
• request-promise-native: Replace deprecated package request-promise-native #298

[cgewecke]

Closing via #299, #297, #296, #295