Style: fix typo.

Signed-off-by: Piotr Sikora <piotr@cloudflare.com>

src/misc/ngx_cpp_test_module.cpp

diff --git a/src/misc/ngx_cpp_test_module.cpp b/src/misc/ngx_cpp_test_module.cpp
index 3cbc0a8..5d2f08d 100644
--- a/src/misc/ngx_cpp_test_module.cpp
+++ b/src/misc/ngx_cpp_test_module.cpp
@@ -1,5 +1,5 @@
 
-// stub module to test header files' C++ compatibilty
+// stub module to test header files' C++ compatibility
 
 extern "C" {
   #include <ngx_config.h>