Updated Syntastic configuration:
* better description. One could argue something like this
should've been done in .vimrc.last in the first place, but I'd
say it's probably useful as a guideline for users new to Syntastic.
* Removed JavaScript and sh from active filetypes. I personally
don't develop anything in JS from day to day, and nothing else
in the configuration empowers JS. Sh was removed since it collides
with 'filetype sh' for .txt. I've removed sh from my personal list
of active filetypes a long time ago, so others would probably do
the same.