Bump up the version of Meson used by AppVeyor

We need a newer version to build Epoxy under CI.

.appveyor.yml

@@ -21,12 +21,12 @@ before_build:
 - mkdir build
 - mkdir libepoxy-shared-%pout%
 - cd build
-- curl -LsSO https://github.com/mesonbuild/meson/releases/download/0.38.0/meson-0.38.0.tar.gz
+- curl -LsSO https://github.com/mesonbuild/meson/releases/download/0.39.1/meson-0.39.1.tar.gz
-- 7z x meson-0.38.0.tar.gz
+- 7z x meson-0.39.1.tar.gz
-- move dist\meson-0.38.0.tar .
+- move dist\meson-0.39.1.tar .
-- 7z x meson-0.38.0.tar
+- 7z x meson-0.39.1.tar
 - rmdir dist
-- del meson-0.38.0.tar meson-0.38.0.tar.gz
+- del meson-0.39.1.tar meson-0.39.1.tar.gz
 - curl -LsSO https://github.com/ninja-build/ninja/releases/download/v1.7.2/ninja-win.zip
 - 7z x ninja-win.zip
 - del ninja-win.zip
@@ -36,7 +36,7 @@ before_build:
 build_script:
 - cd build
 - call "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" %PLATFORM%
-- C:\Python36\python.exe meson-0.38.0\meson.py .. . --backend=ninja --prefix=%APPVEYOR_BUILD_FOLDER%\libepoxy-shared-%pout%
+- C:\Python36\python.exe meson-0.39.1\meson.py .. . --backend=ninja --prefix=%APPVEYOR_BUILD_FOLDER%\libepoxy-shared-%pout%
 - ninja
 - ninja install
 - cd ..