fix average package

chapter5/average/main.go

@@ -1,13 +1,21 @@
 package main
 
-import "fmt"
+import (
+	"fmt"
+	"headfirstgo/headfirstgo/chapter5/datafile"
+	"log"
+)
 
 func main() {
-	numbers := [3]float64{71.8, 56.2, 89.5}
+	numbers, err := datafile.GetFloats("data.txt")
+	if err != nil {
+		log.Fatal(err)
+	}
 	var sum float64 = 0
 	for _, num := range numbers {
 		sum += num
 	}
 
-	fmt.Println(sum)
+	sampleCount := float64(len(numbers))
+	fmt.Printf("Average: %0.2f\n", sum/sampleCount)
 }