Fix style values containing upper-case characters

[zhangbenber]

inlineStyleToObject('background:url(https://test.com/IMAGE.png)') returns:
before: { background: 'url(https://test.com/image.png)' }
after: { background: 'url(https://test.com/IMAGE.png)' }

[coveralls]

Coverage remained the same at 100.0% when pulling 1a64a90 on zhangbenber:fix-style-upper-case into e89bba4 on wrakky:master.

[mrdrogdrog]

@zhangbenber because this repository seems to be rather unmaintained, we at hedgedoc created a hard fork of the library and added some improvements. I would like to add your change to our fork (or you do it yourself with a PR). Are you okay with that?

[zhangbenber]

@zhangbenber because this repository seems to be rather unmaintained, we at hedgedoc created a hard fork of the library and added some improvements. I would like to add your change to our fork (or you do it yourself with a PR). Are you okay with that?

Great. Feel free to do that.

[mrdrogdrog]

Already done. Thanks :)