Switch back to gray-matter for front-matter parsing.

package.json

@@ -106,6 +106,7 @@
     "dateformat": "^1.0.12",
     "deep-equal": "^1.0.1",
     "fuzzy": "^0.1.1",
+    "gray-matter": "^3.0.3",
     "history": "^2.1.2",
     "immutability-helper": "^2.0.0",
     "immutable": "^3.7.6",
@@ -121,9 +122,6 @@
     "moment": "^2.11.2",
     "node-sass": "^3.10.0",
     "normalize.css": "^4.2.0",
-    "preliminaries": "^1.3.0",
-    "preliminaries-parser-toml": "^1.3.0",
-    "preliminaries-parser-yaml": "^1.3.0",
     "prismjs": "^1.5.1",
     "prop-types": "^15.5.10",
     "react": "^15.1.0",
@@ -164,6 +162,7 @@
     "slate-edit-table": "^0.10.1",
     "slate-soft-break": "^0.3.0",
     "slug": "^0.9.1",
+    "toml": "^2.3.3",
     "unified": "^6.1.4",
     "unist-builder": "^1.0.2",
     "unist-util-visit-parents": "^1.1.1",