config: Increase editorconfig's indent size from 2 to 4

I am growing old and can't see that well anymore, so an indentation of 4
really helps my orientation in the source code.

.editorconfig

@@ -6,6 +6,6 @@ root = true
 end_of_line = lf
 insert_final_newline = true
 indent_style = space
-indent_size = 2
+indent_size = 4
 charset = utf-8
 trim_trailing_whitespace = true