Update mount-specs.md (#591)
Update mount-specs.md (#591)

Summary:
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## Changelog

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Pull Request resolved: https://github.com/facebook/litho/pull/591

Test Plan:
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Reviewed By: astreet

Differential Revision: D18222929

Pulled By: adityasharat

fbshipit-source-id: 5fd45ee537c08699a15cc940e6324fb4c8bb376b

facebook/litho,facebook/litho,facebook/litho,facebook/litho,facebook/litho,facebook/litho