Use curl for downloads in AppVeyor. (#115)

appveyor.yml

@@ -15,8 +15,7 @@ install:
   - ps: pwd
 
   # Install Rust and Cargo
-  - ps: '[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12'
-  - ps: Start-FileDownload https://win.rustup.rs -FileName rustup-init.exe
+  - curl --fail --silent --show-error --location --output rustup-init.exe https://win.rustup.rs
   - rustup-init.exe --default-host %TARGET% --default-toolchain %CHANNEL% -y
   - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
   - rustc -Vv
@@ -27,12 +26,12 @@ install:
   - if "%TARGET%" == "x86_64-pc-windows-gnu" set PATH=%PATH%;C:\msys64\mingw64\bin
 
   # Install SDL2.
-  - ps: Start-FileDownload https://www.libsdl.org/release/SDL2-devel-2.0.5-VC.zip -FileName sdl2.zip
+  - curl --fail --silent --show-error --location --output sdl2.zip https://www.libsdl.org/release/SDL2-devel-2.0.5-VC.zip
   - ps: Expand-Archive sdl2.zip -DestinationPath sdl2
   - set LIB=%LIB%;C:\projects\rust-belt\sdl2\SDL2-2.0.5\lib\x64
 
   # Install SDL2_Mixer.
-  - ps: Start-FileDownload https://www.libsdl.org/projects/SDL_mixer/release/SDL2_mixer-devel-2.0.1-VC.zip -FileName sdl2_mixer.zip
+  - curl --fail --silent --show-error --location --output sdl2_mixer.zip https://www.libsdl.org/projects/SDL_mixer/release/SDL2_mixer-devel-2.0.1-VC.zip
   - ps: Expand-Archive sdl2_mixer.zip -DestinationPath sdl2_mixer
   - set LIB=%LIB%;C:\projects\rust-belt\sdl2_mixer\SDL2_mixer-2.0.1\lib\x64
   - ps: Get-ChildItem -Recurse -Depth 4