[GEXF] use the browser version of graphology-gexf

This will avoid shimming xmldom since the XML APIs
already exist in the browser

src/core/graph/import/index.ts

@@ -1,5 +1,5 @@
 import Graph from "graphology";
-import gexf from "graphology-gexf";
+import gexf from "graphology-gexf/browser";
 import graphml from "graphology-graphml/browser";
 
 import { resetStates } from "../../context/dataContexts";