Fix syntax in RST tables

[mwtoews]

Fixes LaTeX issue in #967 and allows PDF to be built on older sphinx versions (like mine)

[kbevers]

Nice catch. I wonder why Sphinx didn't complain about that here...?

[mwtoews]

Yeah, I'd like to know a better way to parse .rst documents to raise possible errors or warnings. I only found these, and similar (410a515) by inspecting the latex log output to see which document it was parsing, then looking a the .rst document to manually inspect for oddities. There should be a better way to log these somehow...

[kbevers]

Apparently there's rstcheck which seems to do the trick. More or less at least. I'll play around with it a bit. I might make sense to add as a travis check.