Build instructions - small correction suggested

[bluebob]

Following the build instructions gives the following error:

# github.com/akamai/cli-common-golang
github.com/akamai/cli-common-golang/common.go:66:18: cannot use cli.StringFlag literal (type cli.StringFlag) as type cli.Flag in array or slice literal:
	cli.StringFlag does not implement cli.Flag (Apply method has pointer receiver)
github.com/akamai/cli-common-golang/common.go:70:5: unknown field 'EnvVar' in struct literal of type cli.StringFlag
github.com/akamai/cli-common-golang/common.go:72:18: cannot use cli.StringFlag literal (type cli.StringFlag) as type cli.Flag in array or slice literal:
	cli.StringFlag does not implement cli.Flag (Apply method has pointer receiver)
github.com/akamai/cli-common-golang/common.go:76:5: unknown field 'EnvVar' in struct literal of type cli.StringFlag
github.com/akamai/cli-common-golang/common.go:89:16: cannot use commands (type []cli.Command) as type []*cli.Command in assignment
github.com/akamai/cli-common-golang/common.go:92:18: cannot use cli.BoolFlag literal (type cli.BoolFlag) as type cli.Flag in assignment:
	cli.BoolFlag does not implement cli.Flag (Apply method has pointer receiver)
github.com/akamai/cli-common-golang/common.go:97:25: cannot use cli.BoolFlag literal (type cli.BoolFlag) as type cli.Flag in assignment:
	cli.BoolFlag does not implement cli.Flag (Apply method has pointer receiver)
github.com/akamai/cli-common-golang/common.go:101:15: cannot use cli.BoolFlag literal (type cli.BoolFlag) as type cli.Flag in assignment:
	cli.BoolFlag does not implement cli.Flag (Apply method has pointer receiver)
github.com/akamai/cli-common-golang/common.go:145:12: cannot use ctx.App.Commands (type []*cli.Command) as type []cli.Command in assignment
github.com/akamai/cli-common-golang/common.go:149:13: cannot use ctx.Command.Subcommands (type []*cli.Command) as type []cli.Command in assignment
github.com/akamai/cli-common-golang/common.go:149:13: too many errors

This is on Mac Go v1.13.

Ive subsequently made a small change - adding the -d switch to first step in the source build instructions so that the go get only downloads the files. The rest of the build process, starting with dep ensure, then works fine. Can I suggest this as a tiny doc update please?