Bump Zone.js to remove warnings when using angular >=6.

Created by: d0x

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• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
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Description of the PR

Fixed #1506 (closed) . Bump Zone.js peer dependency. Angular 6 and 7 is using Zone.js 0.8.26. I tested zone.js 0.8.26 in our environment with Angular 6.

Since it shouldn't break anything, the current master branch is correct, or?

@Committee: I used the syntax ^0.7.6 || ^0.8.26 to support a wider range of angular versions. What do you think about this?

And why ./bin/typescript-angular-petstore-all.sh doesn't put this syntax into the generated package.jsons?