fix karma test failure (1 import statement)

seems like karma doesn't like the other way of importing, though it worked in OSMD,
when executing the test there directly in npm start

src/MusicalScore/Graphical/GraphicalMusicSheet.ts

@@ -23,7 +23,7 @@ import {CollectionUtil} from "../../Util/CollectionUtil";
 import {SelectionStartSymbol} from "./SelectionStartSymbol";
 import {SelectionEndSymbol} from "./SelectionEndSymbol";
 import {OutlineAndFillStyleEnum} from "./DrawingEnums";
-import { EngravingRules } from ".";
+import {EngravingRules} from "./EngravingRules";
 
 /**
  * The graphical counterpart of a [[MusicSheet]]