Install libsfml-dev on travis.
Install libsfml-dev on travis.

dom96/Nim,russpowers/Nim,dom96/Nim,russpowers/Nim,russpowers/Nim,dom96/Nim,dom96/Nim,dom96/Nim,russpowers/Nim,dom96/Nim,russpowers/Nim,russpowers/Nim,russpowers/Nim,dom96/Nim