techdocs: switch to xhr-based event source polyfill

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

plugins/techdocs/package.json

@@ -45,7 +45,7 @@
     "@material-ui/lab": "4.0.0-alpha.45",
     "@material-ui/styles": "^4.10.0",
     "dompurify": "^2.2.9",
-    "eventsource": "^1.1.0",
+    "event-source-polyfill": "^1.0.25",
     "react": "^16.13.1",
     "react-dom": "^16.13.1",
     "react-lazylog": "^4.5.2",
@@ -65,7 +65,6 @@
     "@testing-library/react-hooks": "^3.4.2",
     "@testing-library/user-event": "^13.1.8",
     "@types/dompurify": "^2.2.2",
-    "@types/eventsource": "^1.1.5",
     "@types/jest": "^26.0.7",
     "@types/node": "^14.14.32",
     "@types/react": "*",