fix race condition for SetFormatter and properly fix SetReportCaller race as well

entry.go

@@ -284,13 +284,13 @@ func (entry *Entry) fireHooks() {
 }
 
 func (entry *Entry) write() {
+	entry.Logger.mu.Lock()
+	defer entry.Logger.mu.Unlock()
 	serialized, err := entry.Logger.Formatter.Format(entry)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "Failed to obtain reader, %v\n", err)
 		return
 	}
-	entry.Logger.mu.Lock()
-	defer entry.Logger.mu.Unlock()
 	if _, err := entry.Logger.Out.Write(serialized); err != nil {
 		fmt.Fprintf(os.Stderr, "Failed to write to log, %v\n", err)
 	}