Merge upstream

AlgorithmVisualizer.wiki @ 1b801396

-Subproject commit dd1dc110d49ba804325e1b0b1650debf493bb28e
+Subproject commit 1b8013960685f24aad4adbebce6765d3bf32477c

js/module/tracer/directed_graph.js

@@ -17,8 +17,8 @@ class DirectedGraphTracer extends Tracer {
     this.color = {
       selected: '#2962ff',
       visited: '#f50057',
-      left: '#000',
-      default: '#888'
+      left: '#616161',
+      default: '#bdbdbd'
     };
 
     if (this.isNew) initView(this);