[Appveyor] Fix host windows check.

Author: metaskills

test/cases/helper_sqlserver.rb

@@ -26,7 +26,7 @@ def host_windows? ; RbConfig::CONFIG['host_os'] =~ /mswin|mingw/ ; end
     def connection_mode_dblib? ; self.class.connection_mode_dblib? ; end
     def connection_mode_odbc? ; self.class.connection_mode_odbc? ; end
     def sqlserver_azure? ; self.class.sqlserver_azure? ; end
-    def host_windows? ; self.host_windows? ; end
+    def host_windows? ; self.class.host_windows? ; end
 
     def connection
       ActiveRecord::Base.connection