Added backtick to fix formatting

[TheOnlyMerlin]

Brief description of the changes [REQUIRED]

Was missing a backtick in the docs

What browsers and operating systems have you tested these changes on? [REQUIRED]

None, it's a backtick in the docs

Are all automated tests passing? [REQUIRED]

Sure, I assume so, it's a backtick in the docs

Is this pull request against develop or some other non-master branch? [REQUIRED]

Against dev, because I assumed that was preferred vs master. In any case, it's a backtick in docs, add where you will.

See: http://docs.fineuploader.com/branch/master/features/delete.html

[CLAassistant]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

[rnicholus]

Thanks for catching and fixing this! Could you please take a moment to sign the CLA? It sounds silly for a single character change, but I'd like it if all contributors read and sign this document. I will then cherry-pick this change into master and then also merge into develop so we can get stable and in-progress documentation updated.

[rnicholus]

Thanks again for reporting this. I ended up fixing the issue myself directly on master/develop, so I'll close out this PR.