[Snyk] Upgrade core-js from 2.6.5 to 2.6.9

[snyk-bot]

Snyk have raised this PR to upgrade core-js from 2.6.5 to 2.6.9.

• The recommended version is 14 versions ahead of your current version.
• The recommended version was released 3 months ago, on 2019-05-27.

Release notes

• 2.6.9 - 2019-05-27
  • Some fixes and improvements of the postinstall script like support npm color config (#556) or adding support of ADBLOCK env variable
• 2.6.8 - 2019-05-21
  • Added a workaround of a strange npx bug on postinstall, #551
• 2.6.7 - 2019-05-20
  • Added one more workaround of alternative not completely correct Symbol polyfills, #550, #554
• 2.6.6 - 2019-05-19
  • Fixed IE8- non-enumerable properties support in Object.{ assign, entries, values }, #541
  • Fixed support of primitives in Object.getOwnPropertySymbols in Chrome 38 / 39, #539
  • Show a message on postinstall
• 2.6.5 - 2019-02-15

from core-js GitHub Release Notes

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[kingjon3377]

@STOzaki: Sorry for the near-spam; I turned on Snyk's "automatic dependency upgrade PRs" feature, expecting PRs only on my own repos and maybe utopia-airlines ones ... For any given PR, I recommend making sure that it's also trying to add Snyk as a dependency. (This one looks OK, but the minimal documentation suggested it would do that in its PRs.)

[kingjon3377]

I've just "deactivated" your repos in my Snyk dashboard, so there should only be any future Snyk dependency-upgrade PRs if you give it access to your account.