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/command_completion.cpp b/tests/command_completion.cpp
index d439394..9ab146e 100644
--- a/tests/command_completion.cpp
+++ b/tests/command_completion.cpp
@@ -6,7 +6,7 @@
  *
 */
 
-#include "trompeloeil_doctest.h"
+#include "trompeloeil_doctest.hpp"
 #include "parser.hpp"
 #include "pretty_printers.hpp"
 #include "static_schema.hpp"