Adds support for Node version >=12

[agbilotia1998]

Fixes #346

[agbilotia1998]

@simonweniger please review, adding this comment in case auto review request is not created. Thanks :)

[simonweniger]

@troggy can you review this ?

[TheReturnOfJan]

Looks good!

Review steps:

1. I checkout latest master, ran yarn with node 11 and it worked fine.
2. I switched to node 12, and got an error after running yarn.
3. I checked-out this branch.
4. Ran yarn and yarn test on both node 11 and node 12, both working fine.

[agbilotia1998]

@simonweniger I've submitted this as work on Gitcoin, please have a look. Thanks :)

[simonweniger]

@agbilotia1998 payout done, thank you for the contribution. We would love to have you as a contributor. So pleas check other available bountys at leapdao.org/earn. You also will recive LeapTokens as a reputation payment, so make sure you aktivate them in your wallet. This is the Leap Token adress: 0x78230e69d6e6449db1e11904e0bd81c018454d7a

[agbilotia1998]

I've added Leap Token to my account, sure I'll have a look at other bounties as well. Thanks :)

[troggy]

I've found one side effect for using leap-node with node 12.

leap-node uses keccak package via ethereumjs-util package. This package supports native builds (via node-gyp) and falls back to pure JS implementation if it fails to compile native build on install. What I've noticed is that keccak native build always fails for node 12, so pure js implementation will always be used. I'm not sure what are implications of this, probably only possible performance degradation?

Related issue: cryptocoinjs/keccak#10 (resolved in keccak@2.1.0, but latest ethereumjs-util still uses older version)

/cc @TheReturnOfJan

[troggy]

How to check:

if your installation uses js implementation of keccak you will see this on startup: Keccak bindings are not compiled. Pure JS implementation will be used.