Prepare a release of 7.0.2

[jonasfj]

pub.dev would love to get the fix for https://github.com/dart-lang/markdown/issues/521

[isoos]

Note: the bug is blocking the upgrade of dartdoc, which is also needed for new Dart language features.

[srawlins]

I believe you need to bump lib/src/version.dart as well.

[coveralls]

Pull Request Test Coverage Report for Build 4565005686

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 96.066%

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Totals
Change from base Build 4247833014:	0.0%
Covered Lines:	1392
Relevant Lines:	1449

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💛 - Coveralls