Update cos_defines.h

update version to v5.5.1

Author: jackyding2679

include/cos_defines.h

@@ -11,7 +11,7 @@
 
 namespace qcloud_cos {
 
-#define COS_CPP_SDK_VERSON "v5.5.0"
+#define COS_CPP_SDK_VERSON "v5.5.1"
 
 /// 路径分隔符
 const std::string kPathDelimiter = "/";