Change testrpc dependency for ganache-cli.

[jurajpiar]

Currently this uses an old testrpc dependency, which should be changed to ganache-cli.
One of the issues this would resolve is related to the testrpc package having webpack as a direct dependency, which causes problems in projects that require webpack of higher version. Ganache-cli solves this by putting its webpack dep. in dev dependencies.

I've ran the tests with ganach-cli without failing, so if you like I can create a PR.

[sambacha]

an example of how this is creating weird dependencies:

[email protected]
└─┬ [email protected]
  └─┬ @ethereum-waffle/[email protected]
    └─┬ @ethereum-waffle/[email protected]
      └─┬ @ensdomains/[email protected]
        └── [email protected]

[chancehudson]

This is a very simple fix that is causing real issues in downstream projects. Could someone review #334? The problem is literally solved.