Fix panic return type

Signed-off-by: Marcos Lilljedahl <marcosnils@gmail.com>

entry.go

@@ -100,7 +100,7 @@ func (entry Entry) log(level Level, msg string) {
 	// panic() to use in Entry#Panic(), we avoid the allocation by checking
 	// directly here.
 	if level <= PanicLevel {
-		panic(entry)
+		panic(&entry)
 	}
 }