feat(yaml): support comments (#3529)

packages/netlify-cms-core/package.json

@@ -35,7 +35,6 @@
     "history": "^4.7.2",
     "immer": "^3.1.3",
     "js-base64": "^2.5.1",
-    "js-yaml": "^3.12.2",
     "jwt-decode": "^2.1.0",
     "node-polyglot": "^2.3.0",
     "prop-types": "^15.7.2",
@@ -67,7 +66,8 @@
     "semaphore": "^1.0.5",
     "tomlify-j0.4": "^3.0.0-alpha.0",
     "url": "^0.11.0",
-    "what-input": "^5.1.4"
+    "what-input": "^5.1.4",
+    "yaml": "^1.8.3"
   },
   "peerDependencies": {
     "@emotion/core": "^10.0.9",