v7.0.0-alpha.1

Includes all changes from 6.3.2

• support babel-core@7 (#403) (Henry Zhu)
• Use yarn (#376) (Daniel Tschinder)
• chore(package): update babel-plugin-istanbul to version 4.0.0 (#374) (greenkeeper[bot])
• chore(package): update cross-env to version 3.1.4 (#353) (greenkeeper[bot])
• chore(ci): get rid of node 0.10 (#354) (Yuta Hiroto)
• chore(package): update ava to version 0.18.0 (#369) (greenkeeper[bot])