support babel-core@7

[hzoo]

For testing 7, will do a 7.0.0-alpha.1

[codecov]

Codecov Report

Merging #403 into 7.0 will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              7.0     #403   +/-   ##
=======================================
  Coverage   81.87%   81.87%           
=======================================
  Files           6        6           
  Lines         160      160           
  Branches       35       35           
=======================================
  Hits          131      131           
  Misses         13       13           
  Partials       16       16

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