Rename .h header files to .hpp

Majority of the project uses .hpp and .h shouldn't be used for C++
header files anyway.

Change-Id: I979ba2d243f8f5dbf45c37237ac4aaf9a733eba8
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 34c6fb2..28b0163 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -158,7 +158,7 @@
 
     add_library(DoctestIntegration STATIC
         tests/doctest_integration.cpp
-        tests/trompeloeil_doctest.h
+        tests/trompeloeil_doctest.hpp
         tests/wait-a-bit-longer.cpp
         )
     target_include_directories(DoctestIntegration PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/tests/ ${CMAKE_CURRENT_SOURCE_DIR}/src/)