doc: update version info in README (#347)

Author: Berrysoft

README.md

@@ -38,7 +38,7 @@ They don't support Windows.
 Add `compio` as dependency:
 
 ```
-compio = { version = "0.12.0", features = ["macros"] }
+compio = { version = "0.13.0", features = ["macros"] }
 ```
 
 Then we can use high level APIs to perform filesystem & net IO.