Travis-CI : Added dev packages which might just fix the build

Signed-off-by: Gabriel Ravier <gabravier@gmail.com>

.travis.yml

@@ -31,15 +31,25 @@ addons:
           key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
         - sourceline: 'ppa:ubuntu-toolchain-r/test'
     packages:
-    - clang-9
         - cmake
         - gcc-9
         - g++-9
+        - clang-9
+        - libsdl2-dev
+        - libfreetype6-dev
+        - libfltk-dev
+        - libglew-dev
+        - libxmp-dev
   homebrew:
     packages:
         - cmake
         - gcc@9
         - llvm@9
+        - sdl2
+        - freetype
+        - fltk
+        - glew
+        - libxmp-lite
     update: true
 
 env: