Travis: Use Docker to build for Linux

.travis-deps.sh

@@ -5,35 +5,7 @@ set -x
 
 #if OS is linux or is not set
 if [ "$TRAVIS_OS_NAME" = "linux" -o -z "$TRAVIS_OS_NAME" ]; then
-    export CC=gcc-6
-    export CXX=g++-6
-    mkdir -p $HOME/.local
-
-    if [ ! -e $HOME/.local/bin/cmake ]; then
-        echo "CMake not found in the cache, get and extract it..."
-        curl -L http://www.cmake.org/files/v3.6/cmake-3.6.3-Linux-x86_64.tar.gz \
-            | tar -xz -C $HOME/.local --strip-components=1
-    else
-        echo "Using cached CMake"
-    fi
-
-    if [ ! -e $HOME/.local/lib/libSDL2.la ]; then
-        echo "SDL2 not found in cache, get and build it..."
-        wget http://libsdl.org/release/SDL2-2.0.5.tar.gz -O - | tar xz
-        cd SDL2-2.0.5
-        ./configure --prefix=$HOME/.local
-        make -j4 && make install
-    else
-        echo "Using cached SDL2"
-    fi
-
-    export DEBIAN_FRONTEND=noninteractive
-    # Amazing placebo security
-    curl http://apt.llvm.org/llvm-snapshot.gpg.key | sudo -E apt-key add -
-    sudo -E add-apt-repository "deb http://apt.llvm.org/trusty/ llvm-toolchain-trusty-3.9 main"
-    sudo -E apt-get -yq update
-    sudo -E apt-get -yq install clang-format-3.9
-
+    docker pull ubuntu:16.04
 elif [ "$TRAVIS_OS_NAME" = "osx" ]; then
     brew update
     brew install qt5 sdl2 dylibbundler p7zip