Update linkify version

Fixes https://github.com/vector-im/vector-web/issues/2357
In addition, https://github.com/matrix-org/matrix-react-sdk/pull/500 will make sure failures like this are obvious.

package.json

@@ -46,7 +46,7 @@
     "gemini-scrollbar": "matrix-org/gemini-scrollbar#b302279",
     "gfm.css": "^1.1.1",
     "highlight.js": "^9.0.0",
-    "linkifyjs": "2.0.0-beta.4",
+    "linkifyjs": "^2.1.1",
     "matrix-js-sdk": "matrix-org/matrix-js-sdk#develop",
     "matrix-react-sdk": "matrix-org/matrix-react-sdk#develop",
     "modernizr": "^3.1.0",