Pin posthog version

We'd like to manually review each posthog change to avoid unanticipated tracking leakages;
each upgrade should include reviewing the data coming in on events

package.json

@@ -87,7 +87,7 @@
     "pako": "^2.0.3",
     "parse5": "^6.0.1",
     "png-chunks-extract": "^1.0.0",
-    "posthog-js": "^1.12.1",
+    "posthog-js": "1.12.1",
     "prop-types": "^15.7.2",
     "qrcode": "^1.4.4",
     "re-resizable": "^6.9.0",