LinkableLineNumbers doesn't respect WithClasses configuration

[plumbis]

Describe the bug
When using both LinkableLineNumbers(true) and WithClasses(true) the html generated by LinkableLineNumbers always includes a style instead of a class for the style of the line number link.

https://github.com/alecthomas/chroma/blob/master/formatters/html/html.go#L353

To Reproduce
I think this can be reproduced with any code input:

wget http://www.google.com

But the Chroma CLI doesn't have a build with Linkable line numbers yet.

I think a full command would be:

chroma --lexer shell --formatter html --style monokai --html-lines --html-only --html-linkable-lines <source>

Here is the HTML output generated by Hugo demonstrating the problem

<table class="lntable"><tr><td class="lntd">
  <pre tabindex="0" class="chroma"><code><span class="lnt" id="1">
<a style="outline: none; text-decoration:none; color:inherit" href="#1"> 1</a>

Although the table and td elements have classes the a element has an inline style.

I apologize I don't know Golang so I can't test or submit a patch, but it looks like the style needs to be applied similar to highlighted lines here:
https://github.com/alecthomas/chroma/blob/master/formatters/html/html.go#L293

[alecthomas]

Thanks for the excellent bug report, this should be fixed in #692.