Update php version number to 3.4.0

php/ext/google/protobuf/protobuf.h

@@ -37,7 +37,7 @@
 #include "upb.h"
 
 #define PHP_PROTOBUF_EXTNAME "protobuf"
-#define PHP_PROTOBUF_VERSION "3.3.4"
+#define PHP_PROTOBUF_VERSION "3.4.0"
 
 #define MAX_LENGTH_OF_INT64 20
 #define SIZEOF_INT64 8