content: tweak making-slices example for readability

Adding a bit of whitespace makes the code example more scannable.

Change-Id: Ib8cc8ff2847c3e89d1cd1fcf1e6a0a0aaa562e81
Reviewed-on: https://go-review.googlesource.com/19401
Reviewed-by: Andrew Gerrand <adg@golang.org>
diff --git a/content/moretypes/making-slices.go b/content/moretypes/making-slices.go
index 894ee65..2dae8de 100644
--- a/content/moretypes/making-slices.go
+++ b/content/moretypes/making-slices.go
@@ -7,10 +7,13 @@
 func main() {
 	a := make([]int, 5)
 	printSlice("a", a)
+
 	b := make([]int, 0, 5)
 	printSlice("b", b)
+
 	c := b[:2]
 	printSlice("c", c)
+
 	d := c[2:5]
 	printSlice("d", d)
 }