Update binary SDK version for AppVeyor

Author: weltling

.appveyor.yml

@@ -17,7 +17,7 @@ environment:
         PHP_BUILD_CACHE_BASE_DIR: c:\build-cache  
         PHP_BUILD_OBJ_DIR: c:\obj
         PHP_BUILD_CACHE_SDK_DIR: c:\build-cache\sdk
-        PHP_BUILD_SDK_BRANCH: php-sdk-2.1.8
+        PHP_BUILD_SDK_BRANCH: php-sdk-2.1.9beta1
         # ext and env setup for tests
         #MYSQL_TEST_PASSWD: Password12!
         #MYSQL_TEST_USER: root