appveyor - guess where the sln might be

appveyor.yml

@@ -9,7 +9,7 @@ before_build:
   - cmd: cmake -G "Visual Studio 15 Win64" ..
 
 build:
-  project: $(APPVEYOR_BUILD_FOLDER)\$(APPVEYOR_PROJECT_NAME).sln
+  project: $(APPVEYOR_BUILD_FOLDER)\tmp\$(APPVEYOR_PROJECT_NAME).sln
 
 test_script:
   - cmd: ctest -VV -C "Release"