Wrong syntax highlighting for terminal output

[LukasKalbertodt]

Most code blocks that contain output from the terminal seem to be written with

```bash     -or-      ```sh

This results in strange syntax highlighting (here, for example; for in written text is blue). Usually the text in those blocks is just output of rustc or cargo. Syntax-highlighting that doesn't really make sense. bash and sh highlighter are for scripts.

I don't know what chapters this applies to, but there seem to be a few.

[carols10cents]

Yup... this is a hack because i want a gray background for code blocks (even those without syntax highlighting) but it's going to require a modification to mdbook which I haven't been prioritizing very high since this only affects the online version, not the print version. I do want to fix this though!

[carols10cents]

Thank you Lukas-- this issue was just the nudge I needed to get all the pieces together. This should be fixed on the rendered version as soon as travis rebuilds it :)