fix annotate test in C++ mode

tests/run/annotate_html.pyx

@@ -2,7 +2,7 @@
 >>> import os.path as os_path
 >>> module_path = os_path.join(os_path.dirname(__file__), os_path.basename(__file__).split('.', 1)[0])
 >>> assert module_path.endswith('annotate_html')
->>> assert os_path.exists(module_path + '.c'), module_path
+>>> assert os_path.exists(module_path + '.c') or os_path.exists(module_path + '.cpp'), module_path
 >>> assert os_path.exists(module_path + '.html'), module_path
 
 >>> with open(module_path + '.html') as html_file: