build: update editorconfig to resolve a deprecated warning (#5307)

This resolves a deprecated warning when installing prettier.

[image](https://user-images.githubusercontent.com/20282546/47603753-0995a700-da0e-11e8-9c89-61e0ff3d13c9.png)

package.json

@@ -26,7 +26,7 @@
     "dedent": "0.7.0",
     "diff": "3.2.0",
     "domhandler": "2.4.2",
-    "editorconfig": "0.15.0",
+    "editorconfig": "0.15.2",
     "editorconfig-to-prettier": "0.0.6",
     "emoji-regex": "6.5.1",
     "escape-string-regexp": "1.0.5",