Add missing package to dependency checker for arch linux

I added the missing dependency sdl2_ttf for arch linux in the dependency checker as after using the checker I still needed to manually install that to compile.

Author: 2kbits

.travis/deps.sh

@@ -17,6 +17,7 @@ install_arch_linux() {
     sudo pacman -S --noconfirm mesa
     sudo pacman -S --noconfirm libsm
     sudo pacman -S --noconfirm cmake
+    sudo pacman -S --noconfirm sdl2_ttf
 
 }