Update gtest v1.14.0 to v1.15.0

Author: vitalybuka

cmake/external/googletest.cmake

@@ -44,7 +44,7 @@ include (ExternalProject)
 ExternalProject_Add(${GTEST_TARGET}
     PREFIX ${GTEST_TARGET}
     GIT_REPOSITORY https://github.com/google/googletest.git
-    GIT_TAG v1.14.0
+    GIT_TAG v1.15.0
     UPDATE_COMMAND ""
     CMAKE_CACHE_ARGS -DCMAKE_C_COMPILER:FILEPATH=${CMAKE_C_COMPILER}
                      -DCMAKE_CXX_COMPILER:FILEPATH=${CMAKE_CXX_COMPILER}