Use the oldest supported wayland-protocol for CI

Closes #1151.

.travis.yml

@@ -53,10 +53,14 @@ script:
     - if grep -Inr '\s$' src include docs tests examples CMake *.md .gitattributes .gitignore; then echo Trailing whitespace found, aborting.; exit 1; fi
     - mkdir build
     - cd build
-    - if test -n "${USE_WAYLAND}"; then wget https://mirrors.kernel.org/ubuntu/pool/universe/e/extra-cmake-modules/extra-cmake-modules_5.38.0a-0ubuntu1_amd64.deb; fi
-    - if test -n "${USE_WAYLAND}"; then sudo dpkg -i extra-cmake-modules_5.38.0a-0ubuntu1_amd64.deb; fi
-    - if test -n "${USE_WAYLAND}"; then git clone git://anongit.freedesktop.org/wayland/wayland-protocols; fi
-    - if test -n "${USE_WAYLAND}"; then pushd wayland-protocols; ./autogen.sh --prefix=/usr; make -j; sudo make install; popd; fi
+    - if test -n "${USE_WAYLAND}";
+          then wget https://mirrors.kernel.org/ubuntu/pool/universe/e/extra-cmake-modules/extra-cmake-modules_5.38.0a-0ubuntu1_amd64.deb;
+          sudo dpkg -i extra-cmake-modules_5.38.0a-0ubuntu1_amd64.deb;
+          git clone git://anongit.freedesktop.org/wayland/wayland-protocols;
+          pushd wayland-protocols;
+          git checkout 1.6 && ./autogen.sh --prefix=/usr && make && sudo make install;
+          popd;
+      fi
     - cmake -DCMAKE_VERBOSE_MAKEFILE=ON -DBUILD_SHARED_LIBS=${BUILD_SHARED_LIBS} -DGLFW_USE_WAYLAND=${USE_WAYLAND} ..
     - cmake --build .
 notifications: