Update dependencies, enable pruning for vendor/

So, `dep` got an nice new feature to remove tests and non-go files from
`vendor/`, and this brings the size of the vendor directory from ~300MiB
down to ~20MiB. We don that now.

vendor/golang.org/x/oauth2/internal/token.go

@@ -101,6 +101,7 @@ var brokenAuthHeaderProviders = []string{
 	"https://api.pushbullet.com/",
 	"https://api.soundcloud.com/",
 	"https://api.twitch.tv/",
+	"https://id.twitch.tv/",
 	"https://app.box.com/",
 	"https://connect.stripe.com/",
 	"https://login.mailchimp.com/",
@@ -126,6 +127,9 @@ var brokenAuthHeaderProviders = []string{
 	"https://api.sipgate.com/v1/authorization/oauth",
 	"https://api.medium.com/v1/tokens",
 	"https://log.finalsurge.com/oauth/token",
+	"https://multisport.todaysplan.com.au/rest/oauth/access_token",
+	"https://whats.todaysplan.com.au/rest/oauth/access_token",
+	"https://stackoverflow.com/oauth/access_token",
 }
 
 // brokenAuthHeaderDomains lists broken providers that issue dynamic endpoints.