pin highlight.js as they seem to have broken something in 9.15.2

package.json

@@ -73,7 +73,7 @@
     "gemini-scrollbar": "github:matrix-org/gemini-scrollbar#b302279",
     "gfm.css": "^1.1.1",
     "glob": "^5.0.14",
-    "highlight.js": "^9.13.0",
+    "highlight.js": "9.14.2",
     "is-ip": "^2.0.0",
     "isomorphic-fetch": "^2.2.1",
     "linkifyjs": "^2.1.6",