Use build_script instead of build for appveyor
Use build_script instead of build for appveyor

Using build_script to run cmake --build fixes issues with msbuild
not always finding the correct file formats, etc.

grahamreeds/unittest-cpp,grahamreeds/unittest-cpp,unittest-cpp/unittest-cpp,grahamreeds/unittest-cpp,pjohnmeyer/unittest-cpp,jasonhorsburgh/unittest-cpp,unittest-cpp/unittest-cpp,jasonhorsburgh/unittest-cpp,pjohnmeyer/unittest-cpp,unittest-cpp/unittest-cpp