Issue description updates don't add highlighting classes
I'm going to add some mathematics and some code here:
This math is inline $`a^2+b^2=c^2`$.
```ruby
1.upto(3) do { |i| puts "#{i} time(s)" }
```
This math is inline a^2+b^2=c^2
.
1.upto(3) do { |i| puts "#{i} time(s)" }
These should be rendered as mathematics, and syntax-highlighted using my chosen theme.