Import <strike>,<s> tags (strikethrough) from Evernote

[ianjs]

• Desktop: Added strikethrough markdown codes

I am assuming the ~~ Markdown tags for strikethrough are a relatively recent addition because the import from Evernote replaces them with ( and ) as start and end markers.

This PR is a naive change to simply replace the ( and ) with ~~ and ~~.

It does the trick for importing to Markdown, but still has the same limitations for some edge cases, for example it will be ignored if there is trailing space before the closing ~~. This also happens for other tags such as bold/italic, so there needs to be a more general fix for importing format tags.

[laurent22]

Thanks for the pull request. We are now trying to stick closely to CommonMark for the Markdown flavour we support, and I see that ~~ is not part of the spec: https://talk.commonmark.org/t/strikeout-threw-out-strikethrough-strikes-out-throughout/820

In this case what we do is use HTML instead, so would you mind replacing ~~ by <s> </s>?

[ianjs]

Erk. Did this break the build? It seemed to work fine locally as I tested it with an import from ENEX.

If you could let me know how to run the tests locally I'll check.

[laurent22]

The test error was my mistake, thanks for the update @ianjs!