Replace 1.x scrypt shim of web3-eth-accounts with https://github.com/web3-js/scrypt-shim

[michaelsbradleyjr]

Fixes #3018

[coveralls]

Coverage decreased (-0.07%) to 83.117% when pulling fea7a9b on michaelsbradleyjr:refactor/1.x-scrypt-shim into 7d1b0ea on ethereum:1.x.

[michaelsbradleyjr]

I'm working toward a PR that will further improve the web3-js/scrypt-shim package, should be done soon; hopefully today, maybe tomorrow.

Also, I need to do an experiment, but I'm fairly certain already that the present strategy in web3 to point to "rolling updates" branches on GitHub for web3-js/WebSocket-Node and web3-js/scrypt-shim is somewhat flawed. That is, I believe web3 users' package-lock.json or yarn.lock files pin to a specific commit and then later updates will require manual intervention (in the lockfiles!). Instead, I think those packages should be published on the registry, scoped as @web3-js or whatever is appropriate/possible, and when changes are made to them new versions should be published as usual. If we want to stick with pointing to GitHub for those packages, then I believe we should use tags in the github: specifiers rather than a branch name that's always the same, i.e. a new tag can be created when there's an update.