Update to babylon@7.0.0-beta.0

[hzoo]

We need to fix all of the breaking AST changes to pass

remind me not to squash merge

[mention-bot]

@hzoo, thanks for your PR! By analyzing the history of the files in this pull request, we identified @dlwalsh, @loganfsmyth and @forivall to be potential reviewers.

[codecov-io]

Codecov Report

Merging #5317 into 7.0 will increase coverage by 0.16%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              7.0    #5317      +/-   ##
==========================================
+ Coverage   89.88%   90.05%   +0.16%     
==========================================
  Files         200      200              
  Lines        9884     9972      +88     
  Branches     2668     2708      +40     
==========================================
+ Hits         8884     8980      +96     
+ Misses       1000      992       -8

Impacted Files	Coverage Δ
...ckages/babel-types/src/definitions/experimental.js	100% <ø> (ø)	✅
packages/babel-types/src/definitions/es2015.js	100% <ø> (ø)	✅
packages/babel-generator/src/generators/types.js	100% <ø> (+5.06%)	✅
...kages/babel-generator/src/generators/statements.js	99.44% <100%> (-0.01%)	❌
...babel-helper-remap-async-to-generator/src/index.js	94.44% <100%> (+0.07%)	✅
packages/babel-types/src/definitions/flow.js	100% <100%> (ø)	✅
packages/babel-generator/src/generators/flow.js	98.25% <100%> (ø)	✅
...ges/babel-plugin-transform-decorators/src/index.js	71.05% <ø> (+53.81%)	✅

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