String() should return the compact string format by default (#97)

Author: git-hulk

README.md

@@ -55,7 +55,7 @@ if err != nil {
 
 // Call the String method to unparsed AST into a SQL string
 for _, stmt := range statements {
-  fmt.Println(stmt.String(0 /* number of tab spaces*/))
+  fmt.Println(stmt.String())
 }
 ```
 ## Update test assets

main.go

@@ -65,7 +65,7 @@ func main() {
 		fmt.Println(string(bytes))
 	} else { // format SQL
 		for _, stmt := range stmts {
-			fmt.Println(stmt.String(0))
+			fmt.Println(stmt.String())
 		}
 	}
 }