Add checkdate func

Syyong · Syyong · commit d181fd63dc89 · 2018-08-24T12:43:48.000+08:00
diff --git a/README.md b/README.md
@@ -12,6 +12,7 @@ go get github.com/syyongx/php2go
 time()
 strtotime()
 date()
+checkdate()
 sleep()
 usleep()
 ```
