Fix org-src-lang-modes

[ag91]

Hey thanks for this mode: it is very useful at work!!

The org-src-lang-modes list contains cons-cell with symbols, not strings: (("amm" . scala) ("arduino" . arduino) ("translate" . text) ("redis" . redis) ("php" . php) ("C" . c) ("C++" . c++) ("asymptote" . asy) ("bash" . sh) ...)

It was causing Wrong type argument: symbolp, "ob-http" on tangling snippets.