Misspelling in MD003

[henrikh]

Fixed misspelling in description of rule MD003.

[coveralls]

Coverage remained the same at 100.0% when pulling 3834cc4 on henrikh:MD003-misspelling into 82d9c36 on DavidAnson:master.

[DavidAnson]

Thank you, I'll merge this tonight!

[DavidAnson]

However, I need to understand the CI failures first. Not your fault, but maybe a breaking change in markdown-it 8.3.2: https://github.com/markdown-it/markdown-it/blob/master/CHANGELOG.md

[DavidAnson]

Confirmed there is a behavior change between:

• markdown-it@8.3.2
• markdown-it@8.4.0

package.json has "markdown-it": "^8.3.1", so 8.4.0 is being installed by CI.

This breaks the markdownlint tests per CI above. I'll address this break before accepting the PR.

Thanks for your patience!