Update babel-core dependency to v7 for jest-config

[matthamil]

Resolves #6913

Summary

I was seeing the same error as reported in #6913. I had babel-core@7.0.0-bridge.0 installed locally. I noticed that inside my node_modules/jest-config directory, it installed babel-core@6.26.3 inside its node_modules. I traced this back to the package.json file specifying "babel-core": "^6.0.0" which does not allow for usage of babel-core@7.0.0-bridge.0, so npm will install the latest 6.* version of babel-core. When you run your tests, you get the same error as seen in #6913.

npm ls
# truncated output to show problem
├─┬ jest-config@23.5.0
│   │ ├─┬ babel-core@6.26.3
│   │ │ ├── babel-code-frame@6.26.0 deduped
│   │ │ ├── babel-generator@6.26.0 deduped
│   │ │ ├─┬ babel-helpers@6.24.1
│   │ │ │ ├── babel-runtime@6.26.0 deduped
│   │ │ │ └── babel-template@6.26.0 deduped
│   │ │ ├── babel-messages@6.23.0 deduped
│   │ │ ├─┬ babel-register@6.26.0
│   │ │ │ ├─┬ babel-core@6.26.3

If you have babel-core@7.0.0-bridge.0 installed in your package.json, this will still be ignored by jest-config as it installs an older version.

Test plan

Using npm version 6.1.0, download jest via npm install jest --save-dev. Install babel-core@7.0.0-bridge.0 as well. Dig through node_modules/jest-config/node_modules to see if it installed v6.26.3 of babel-core.

[codecov-io]

Codecov Report

Merging #6926 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #6926   +/-   ##
=======================================
  Coverage   66.97%   66.97%           
=======================================
  Files         250      250           
  Lines       10378    10378           
  Branches        3        3           
=======================================
  Hits         6951     6951           
  Misses       3426     3426           
  Partials        1        1

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[milesj]

IMO, a better solution would be to upgrade the entire Babel suite in Jest to v7.

[matthamil]

@milesj I agree. I made this change under the assumption that the rest of the packages were using babel 7 since I didn't see any errors in my console after making this change. After poking around, some packages are still listing a 6.* version in their package.json.

[matthamil]

Closing in favor of #6949

Thanks @milesj for picking that up! :)

[github-actions]

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