chore: update .gitignore to exclude _example files (#141)

Signed-off-by: Flc <four_leaf_clover@foxmail.com>

Author: flc1125

.gitignore

@@ -17,4 +17,5 @@ vendor/
 .tools
 .todo
 *_prod_test.go
-!api_types_test.go
+!api_types_test.go
+_example