Merge pull request zcash#6967 from daira/fix-test_checkblock

gtest/test_checkblock.cpp: fix a bug in MockCValidationState that was causing a test warning

Author: str4d

src/gtest/test_checkblock.cpp

@@ -10,7 +10,7 @@
 class MockCValidationState : public CValidationState {
 public:
     MOCK_METHOD6(DoS, bool(int level, bool ret,
-             unsigned int chRejectCodeIn, const std::string strRejectReasonIn,
+             unsigned int chRejectCodeIn, const std::string &strRejectReasonIn,
              bool corruptionIn,
              const std::string &strDebugMessageIn));
     MOCK_METHOD4(Invalid, bool(bool ret,