Make plausible detection actually robust

src/lib/plausible.js

@@ -1,6 +1,6 @@
 // Some ad-blockers block the plausible script from loading. Check if `plausible`
 // is defined before calling it.
 export function tryPlausible(msg) {
-	if (plausible)
+	if (self.plausible)
 		plausible(msg)
 }