Update Ninja download url due to Dropbox changes.

.appveyor.yml

@@ -38,7 +38,7 @@ branches:
 install:
   # Use the x86 python only when building for x86 for the cpython tests.
   # For all other archs (including, say, arm), use the x64 python.
-  - ps: (new-object net.webclient).DownloadFile('https://dl.dropboxusercontent.com/u/37517477/ninja.exe', 'C:\projects\meson\ninja.exe')
+  - ps: (new-object net.webclient).DownloadFile('https://www.dropbox.com/s/bbzvepq85hv47x1/ninja.exe?dl=0', 'C:\projects\meson\ninja.exe')
   - cmd: if %arch%==x86 (set MESON_PYTHON_PATH=C:\python34) else (set MESON_PYTHON_PATH=C:\python34-x64)
   - cmd: echo Using Python at %MESON_PYTHON_PATH%
   - cmd: if %compiler%==msvc2010 ( call "C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\vcvarsall.bat" %arch% )