Update appvayor ci for ogg library name changes.

Unbreaks test builds on this service.

The Visual Studio build of the ogg library was changed
recently to build static libraries by default, and the
`_static` name suffix was removed. Reference this target
when building the ogg library debpendency from a git
checkout on the Appveyor continuous integration service.

Signed-off-by: Mark Harris <mark.hsj@gmail.com>

.appveyor.yml

@@ -17,7 +17,7 @@ install:
 - 7z x opus.zip -oopus-artifacts
 - move /Y opus-artifacts opus
 - git clone -q https://github.com/xiph/ogg.git ogg
-- msbuild ogg\win32\VS2015\libogg_static.sln /p:Configuration=%CONFIGURATION:-NoHTTP=%;Platform=%PLATFORM% /m /v:minimal /logger:"C:\Program Files\AppVeyor\BuildAgent\Appveyor.MSBuildLogger.dll"
+- msbuild ogg\win32\VS2015\libogg.sln /p:Configuration=%CONFIGURATION:-NoHTTP=%;Platform=%PLATFORM% /m /v:minimal /logger:"C:\Program Files\AppVeyor\BuildAgent\Appveyor.MSBuildLogger.dll"
 - if %CONFIGURATION:-NoHTTP=%==%CONFIGURATION% git clone -q --branch=OpenSSL_1_0_2-stable https://github.com/openssl/openssl.git openssl
 - ps: >-
         If ($env:Platform -Match "Win32") {