fix config in babel 7

[gengjiawen]

Summary

• Fix ast is null in babel 7, see facebook/react-native@f8d6b97#r28647044.

• change sourceType to "unambiguous", see facebook/react-native@f8d6b97#r28569395.

With those change, react native can fix all jest test.

Test Suites: 2 skipped, 100 passed, 100 of 102 total
Tests:       4 skipped, 553 passed, 557 total
Snapshots:   37 passed, 37 total
Time:        78.455s
Ran all test suites.
Done in 79.46s.

Test plan

pass react native test-ci task.

[codecov-io]

Codecov Report

Merging #162 into master will decrease coverage by 0.01%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master     #162      +/-   ##
==========================================
- Coverage   81.15%   81.13%   -0.02%     
==========================================
  Files         126      126              
  Lines        4520     4522       +2     
==========================================
+ Hits         3668     3669       +1     
- Misses        852      853       +1

Impacted Files	Coverage Δ
packages/metro/src/transformer.js	89.79% <50%> (-1.7%)	⬇️

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[gengjiawen]

@rafeca Can you review this pr ? Thanks.

[gengjiawen]

@qfox Can you take a look at this pr, set options on preprocessor won't work.

[pvdz]

@gengjiawen this problem should be resolved once the lockdown lands. For now your workaround is to manually and explicitly install babel at 7.0.0-beta.40

These api changes were added later (which is why they slipped under our radar). The lockdown fixes will hopefully be published in a new version today.

Note that if you still require the BABEL_VERSION flag to be set at all then you're using an older version of Metro. Regardless, to fix the option problem you'll need to wait a few hours. Working hard on it.

[gengjiawen]

Okay, but add options like this facebook/react-native@da57ae7 won't work, because inside metro won't accept option like this.

[gengjiawen]

I hope we can fix the ci thing soon :)

[rafeca]

@qfox is this PR still relevant with your latest changees?