Update import to v2 in doc example

Author: loganrosen

doc.go

@@ -16,7 +16,7 @@ Usage Example:
 	    import (
 	        "fmt"
 
-	        "github.com/linkedin/goavro"
+	        "github.com/linkedin/goavro/v2"
 	    )
 
 	    func main() {