Upgrade method to latest core spec

[rado0x54]

Version 12/08/2020: https://www.w3.org/TR/2020/WD-did-core-20201108/

Changes to current:

• DID Controller
• assertionMethod
• keyAgreement
• Key types and formats
• publicKeyJwk
• publicKeyBase58
• JsonWebKey2020
• EcdsaSecp256k1RecoveryMethod2020

[rado0x54]

Use this feature to double check (maybe outdated) feedback from #21

[uport-automation-bot]

:tada: This issue has been resolved in version 2.0.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: