appveyor: Use the correct ogg solution file.

In ogg commit 6d55ddf64b65, the static build was made the
default, removing the separate static target solution file,
breaking our build on the Appveyor continuous integration system.

appveyor.yml

@@ -12,7 +12,7 @@ environment:
 
 install:
 - git clone -q https://github.com/xiph/ogg.git %APPVEYOR_BUILD_FOLDER%\..\libogg
-- if "%BUILD_SYSTEM%"=="MSVC" msbuild "%APPVEYOR_BUILD_FOLDER%\..\libogg\win32\VS2015\libogg_static.sln" /m /v:minimal /logger:"C:\Program Files\AppVeyor\BuildAgent\Appveyor.MSBuildLogger.dll" /property:Configuration=%CONFIGURATION%;Platform=%PLATFORM%
+- if "%BUILD_SYSTEM%"=="MSVC" msbuild "%APPVEYOR_BUILD_FOLDER%\..\libogg\win32\VS2015\libogg.sln" /m /v:minimal /logger:"C:\Program Files\AppVeyor\BuildAgent\Appveyor.MSBuildLogger.dll" /property:Configuration=%CONFIGURATION%;Platform=%PLATFORM%
 - if "%BUILD_SYSTEM%"=="CMAKE" mkdir "%APPVEYOR_BUILD_FOLDER%\..\libogg\build"
 - if "%BUILD_SYSTEM%"=="CMAKE" pushd "%APPVEYOR_BUILD_FOLDER%\..\libogg\build"
 - if "%BUILD_SYSTEM%"=="CMAKE" cmake -A "%PLATFORM%" -G "Visual Studio 14 2015" -DCMAKE_INSTALL_PREFIX="%APPVEYOR_BUILD_FOLDER%\..\libogg\install" ..