chore(deps): Bump highlight.js to known working version (#1210)

Author: tmcw

package.json

@@ -44,7 +44,7 @@
     "github-slugger": "1.2.0",
     "glob": "^7.1.2",
     "globals-docs": "^2.4.0",
-    "highlight.js": "^9.12.0",
+    "highlight.js": "^9.15.5",
     "js-yaml": "^3.10.0",
     "lodash": "^4.17.10",
     "mdast-util-inject": "^1.1.0",