(appveyor) Use PHP 7.0.16

appveyor.yml

@@ -8,7 +8,7 @@ environment:
     OUTDIR: Release
     CONFIGURE_EXTRA: --disable-zts
 
-  PHP_VERSION: 7.0.7
+  PHP_VERSION: 7.0.16
   PHP_SDK: c:\projects\php-sdk
 
 os: Windows Server 2012