Revert "Removed sfml-network from travis build."
Revert "Removed sfml-network from travis build."

This reverts commit 92e44f4952f499952de3506b8672e20f0b51fd31. Commit intended to remove sfml-network from build, but network component is build by 'make install' anyways.

namelessvoid/qrwar,namelessvoid/qrwar