Trying to download and build GLFW since APT repository are unreliable

.travis.yml

@@ -9,8 +9,19 @@ compiler:
   - clang
 
 before_install:
-  - if [ $TRAVIS_OS_NAME == linux ]; then sudo add-apt-repository -y ppa:pyglfw/pyglfw && sudo apt-get update -qq && sudo apt-get install -y --no-install-recommends libglfw3-dev libxrandr-dev libxi-dev libxxf86vm-dev libsdl2-dev; fi
-  - if [ $TRAVIS_OS_NAME == osx ]; then brew update && brew install glfw3 && brew install sdl2; fi
+  - if [ $TRAVIS_OS_NAME == linux ]; then 
+       sudo apt-get update -qq
+       sudo apt-get install -y --no-install-recommends libxrandr-dev libxi-dev libxxf86vm-dev libsdl2-dev 
+       wget https://github.com/glfw/glfw/releases/download/3.2.1/glfw-3.2.1.zip
+       unzip glfw-3.2.1.zip && cd glfw-3.2.1;
+       cmake -DCMAKE_INSTALL_PREFIX=$HOME -DBUILD_SHARED_LIBS=true -DGLFW_BUILD_EXAMPLES=false -DGLFW_BUILD_TESTS=false -DGLFW_BUILD_DOCS=false .;
+       sudo make -j $CPU_NUM install && cd ..
+    fi
+  - if [ $TRAVIS_OS_NAME == osx ]; then 
+       brew update
+       brew install glfw3
+       brew install sdl2
+    fi
 
 script: 
   - make -C examples/opengl2_example