Update CMakeLists.txt to not use list PREPEND

This isn't supported in 3.14.3, at least, but list INSERT with a 0 index is
equivalent and is available there.

(PR #73 followup)

CMakeLists.txt

@@ -8,7 +8,7 @@ set (CMAKE_CXX_STANDARD 17)
 set (CMAKE_CXX_STANDARD_REQUIRED ON)
 
 # For sanitizers
-list (PREPEND CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake")
+list (INSERT CMAKE_MODULE_PATH 0 "${CMAKE_SOURCE_DIR}/cmake")
 
 # Configuration options