Update exposure.go

Author: eliottness

openfeature/exposure.go

@@ -171,7 +171,7 @@ func (w *exposureWriter) flush() {
 
 	// Move buffer to local variable and create new buffer
 	events := w.buffer
-	w.buffer = make([]exposureEvent, len(events)/2)
+	w.buffer = make([]exposureEvent, 0, len(events)/2)
 	w.mu.Unlock()
 
 	// Build payload