_yarn: fix parsing of yarn run on scripts containing }

[mcornella]

When a package.json script command uses the closing curly brace, the current yarn run parsing fails to capture the whole hints property value, leading to it not parsing correctly the rest of the scripts commands. See #667.

This solution uses the fact that the hints property value always ends with a double quote and a closing curly brace to match the whole property value, disregarding whether a closing curly brace is used in a script command. See #667 (comment).

Fixes #667

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