fix: correctly print disk sizes on 32bit systems (#800)

The order of when the casting occurs is important, or we might overflow.

The bug can be reproduced with:
```
GOARCH=386 go test  ./...
```

internal/cmd/server/describe.go

@@ -112,7 +112,7 @@ var DescribeCmd = base.DescribeCmd{
 				}
 				cmd.Printf("  - ID:\t\t%d\n", volume.ID)
 				cmd.Printf("    Name:\t%s\n", volume.Name)
-				cmd.Printf("    Size:\t%s\n", humanize.Bytes(uint64(volume.Size*humanize.GByte)))
+				cmd.Printf("    Size:\t%s\n", humanize.Bytes(uint64(volume.Size)*humanize.GByte))
 			}
 		} else {
 			cmd.Printf("  No Volumes\n")

internal/cmd/volume/describe.go

@@ -30,7 +30,7 @@ var DescribeCmd = base.DescribeCmd{
 		cmd.Printf("ID:\t\t%d\n", volume.ID)
 		cmd.Printf("Name:\t\t%s\n", volume.Name)
 		cmd.Printf("Created:\t%s (%s)\n", util.Datetime(volume.Created), humanize.Time(volume.Created))
-		cmd.Printf("Size:\t\t%s\n", humanize.Bytes(uint64(volume.Size*humanize.GByte)))
+		cmd.Printf("Size:\t\t%s\n", humanize.Bytes(uint64(volume.Size)*humanize.GByte))
 		cmd.Printf("Linux Device:\t%s\n", volume.LinuxDevice)
 		cmd.Printf("Location:\n")
 		cmd.Printf("  Name:\t\t%s\n", volume.Location.Name)

internal/cmd/volume/list.go

@@ -48,7 +48,7 @@ var ListCmd = base.ListCmd{
 			})).
 			AddFieldFn("size", output.FieldFn(func(obj interface{}) string {
 				volume := obj.(*hcloud.Volume)
-				return humanize.Bytes(uint64(volume.Size * humanize.GByte))
+				return humanize.Bytes(uint64(volume.Size) * humanize.GByte)
 			})).
 			AddFieldFn("location", output.FieldFn(func(obj interface{}) string {
 				volume := obj.(*hcloud.Volume)