chore(deps): update dependency core-js to v2.6.8 - autoclosed

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change	References
core-js	dependencies	patch	2.6.3 -> 2.6.8	source

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Release Notes

zloirock/core-js

### [`v2.6.8`](https://togithub.com/zloirock/core-js/compare/v2.6.7...bab1a285ffc3914f064ab56dbbc2377baab421cc) [Compare Source](https://togithub.com/zloirock/core-js/compare/v2.6.7...bab1a285ffc3914f064ab56dbbc2377baab421cc) ### [`v2.6.7`](https://togithub.com/zloirock/core-js/blob/master/CHANGELOG.md#​267-LEGACY---20190521) [Compare Source](https://togithub.com/zloirock/core-js/compare/v2.6.6...v2.6.7) - Added one more workaround of alternative not completely correct `Symbol` polyfills, [#​550](https://togithub.com/zloirock/core-js/issues/550), [#​554](https://togithub.com/zloirock/core-js/issues/554) ### [`v2.6.6`](https://togithub.com/zloirock/core-js/blob/master/CHANGELOG.md#​266-LEGACY---20190520) [Compare Source](https://togithub.com/zloirock/core-js/compare/v2.6.5...v2.6.6) - Fixed IE8- non-enumerable properties support in `Object.{ assign, entries, values }`, [#​541](https://togithub.com/zloirock/core-js/issues/541) - Fixed support of primitives in `Object.getOwnPropertySymbols` in Chrome 38 / 39, [#​539](https://togithub.com/zloirock/core-js/issues/539) - Show a message on `postinstall` ### [`v2.6.5`](https://togithub.com/zloirock/core-js/blob/master/CHANGELOG.md#​265---20190215) [Compare Source](https://togithub.com/zloirock/core-js/compare/v2.6.4...v2.6.5) - Fixed buggy `String#padStart` and `String#padEnd` mobile Safari implementations, [#​414](https://togithub.com/zloirock/core-js/issues/414). ### [`v2.6.4`](https://togithub.com/zloirock/core-js/blob/master/CHANGELOG.md#​264---20190207) [Compare Source](https://togithub.com/zloirock/core-js/compare/v2.6.3...v2.6.4) - Added a workaround against crushing an old IE11.0.9600.16384 build, [#​485](https://togithub.com/zloirock/core-js/issues/485).

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