Align WebSocket.Frame.encode/2 spec with WebSocket.encode/2

[ColaCheng]

The Mint.WebSocket.shorthand_frame() is missing in the Mint.WebSocket.Frame.encode/2 spec.

[coveralls]

Pull Request Test Coverage Report for Build 87284007604f07b7ccb8cd7ac0c85bfe38fe143a-PR-29

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.3%) to 89.459%

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Totals
Change from base Build d17898b3b37c980e33e9f428b07698312a8cbc85:	0.3%
Covered Lines:	314
Relevant Lines:	351

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💛 - Coveralls

[the-mikedavis]

Ah good catch, thank you!