fix typo

Author: VdustR

packages/doc/docs/index.md

@@ -28,6 +28,6 @@ Transform `.gitignore` to `.dockerignore`.
 
 ## g2d Online
 
-We also provide a online tool to help you transform the `.gitignore` to `.dockerignore` easily.
+We also provide an online tool to help you transform the `.gitignore` to `.dockerignore` easily.
 
 [🚀 Go to the online tool](./online)