v2.0.0

We dropped support for node 4 which dictated the major release.

Changes included in this release:

• Update traviscs yaml for greenkeeper 1e80da8
• Drop node 4 1e80da8
• Update tap to 12.0.1 1e80da8
• Update mock-fs to 4.7.0 1e80da8
• Pin to node 10.4.1 1e80da8
• update eslint to version 5.0.0 e4fc5f2
• update debug to version 4.0.1 e1104b7
• update lodash to version 4.17.11 17dfc7b