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/tests/utils.cpp b/tests/utils.cpp
index 7717480..c862980 100644
--- a/tests/utils.cpp
+++ b/tests/utils.cpp
@@ -6,7 +6,7 @@
  *
 */
 
-#include "trompeloeil_doctest.h"
+#include "trompeloeil_doctest.hpp"
 #include "utils.hpp"
 
 TEST_CASE("utils")