Resolves #178, replace prepend method by a string concatenation

[ggrossetie]

prepend method is not implemented in Opal and will throw an exception at runtime, when using Asciidoctor Reveal.js in a JavaScript environment.

I can confirm that the issue is fixed running the following command:

bundle exec rake build:converter:opal
npm run examples

Resolves #178

[ggrossetie]

To add some context, this issue is blocking.
In a JavaScript environment, if a presentation contains a table, Asciidoctor Reveal.js will throw an exception 😢

@obilodeau Is there anything I can do to help you in order to merge this pull request and release a bugfix version ?

[obilodeau]

I'll check the other pending PR and do a release. Unfortunately, I can't tonight.

Thanks for bringing this up to my attention. I've been busy lately.

[obilodeau]

I'm on Ruby 2.5 here (because arch linux 🤷‍♂️) and there seems to be a problem with either the asciidoctor-template-compiler or the code generated by it. I can't rake build the release now :(

I triggered a build by adding 2.5 to the travis config (hoping it'll work) but I need to go. Once I know where to report the problem or what to change I will. Feel free to take a look in the meantime.

[obilodeau]

Relevant build failure: https://travis-ci.org/asciidoctor/asciidoctor-reveal.js/jobs/335441645

[ggrossetie]

If I recall correctly, @mojavelinux also had troubles upgrading to Ruby 2.5 ?

[mojavelinux]

Ruby 2.5 seems to be causing problems in temple, which is the parser generator used under slim. There's problems using it on Alpine Linux due to stack limits, but where there's smoke, there's fire.

[ggrossetie]

Thanks for bringing this up to my attention. I've been busy lately.

No worries, thanks for the bug fix release 👍