keep 'secret' query parameter first to please the Google Authenticator

[yogo1212]

No description provided.

[yogo1212]

@pquerna could you give this small PR a quick review?
should be an easy merge

[pquerna]

should we use a custom sort here instead of no sorting? i kinda liked it was stable rendering of the input. eg, sort where secret is always first

[pquerna]

something like this?

	slices.SortFunc(keys, func(a, b string) bool {
		if a == "secret" {
			return true
		}
		if b == "secret" {
			return false
		}
		return a < b
	})

[yogo1212]

sure thing - my biggest motivation is to roll out a fix for everyone to enjoy!

i can give you an alternative so you have another option to pick from:

	// Google Authenticator expects the secret to be first, so handle it separately
	keys := make([]string, 0, len(v) - 1)
	for k := range v {
		if k != "secret" {
			keys = append(keys, k)
		}
	}
	sort.Strings(keys)
	for _, k := range append([]string{"secret"}, keys...) {

or maybe a little more optimised:

	// Google Authenticator expects the secret to be first, so handle it separately
	keys := make([]string, 0, len(v))
	keys = append(keys, "secret")
	for k := range v {
		if k != "secret" {
			keys = append(keys, k)
		}
	}
	sort.Strings(keys[1:])
	for _, k := range keys {

these solutions fail, though, if there' no secret at all

[yogo1212]

@pquerna i've amended the commit to keep the sorting in general, as you requested.
i went with the 'one allocation, one comparison in sort' approach.

[yogo1212]

closing this as the investigation over on issue #94 revealed that order of the parameters is not the root cause of the problem.