test: migrate HandlerMock to modern MOCK_METHOD

Replaced legacy MOCK_CONST_METHOD1 macros with modern MOCK_METHOD
to fix below error

'''
test/handler_mock.hpp:18:5: error: There is an unknown macro here somewhere. Configuration is required.
    If GMOCK_PP_CAT is a macro then please configure it. [unknownMacro]
    MOCK_CONST_METHOD1(validIfNameAndField, bool(const std::string&));
'''

Change-Id: I96e3d6970b32aeb20a68605aea29b02853f42d4a
Signed-off-by: Jayanth Othayoth <ojayanth@gmail.com>
diff --git a/test/handler_mock.hpp b/test/handler_mock.hpp
index 1ef94a4..5c2b3cf 100644
--- a/test/handler_mock.hpp
+++ b/test/handler_mock.hpp
@@ -15,8 +15,8 @@
   public:
     ~HandlerMock() = default;
 
-    MOCK_CONST_METHOD1(validIfNameAndField, bool(const std::string&));
-    MOCK_CONST_METHOD1(readStatistic, std::uint64_t(const std::string&));
+    MOCK_METHOD(bool, validIfNameAndField, (const std::string&), (const));
+    MOCK_METHOD(std::uint64_t, readStatistic, (const std::string&), (const));
 };
 
 } // namespace ethstats