Disable indent guides in tree widget (Explorer)

As of VS Code version 1.36 the tree widget support visual indent guide
lines (1) that are enabled by default that have been disabled to
unclutter the UI.

References:
  (1) https://code.visualstudio.com/updates/v1_36#_tree-indent-guides

Resolves GH-210

snowblocks/visual-studio-code/settings.json

@@ -72,6 +72,7 @@
   "workbench.sideBar.location": "left",
   "workbench.startupEditor": "newUntitledFile",
   "workbench.statusBar.feedback.visible": false,
+  "workbench.tree.renderIndentGuides": "none",
 
   /*+--- Extensions ---+*/
   "cSpell.dictionaries": [