internal: remove facebook from brokenAuthHeadersProviders

A friend who now works at Facebook informs me that this is now fixed on their
side. I've asked for some public reference.

Change-Id: I68627e3211f24bc4bea7c698d1126438a0e8ab0d
Reviewed-on: https://go-review.googlesource.com/97055
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: tcolgate

internal/token.go

@@ -103,7 +103,6 @@ var brokenAuthHeaderProviders = []string{
 	"https://api.twitch.tv/",
 	"https://app.box.com/",
 	"https://connect.stripe.com/",
-	"https://graph.facebook.com", // see https://github.com/golang/oauth2/issues/214
 	"https://login.microsoftonline.com/",
 	"https://login.salesforce.com/",
 	"https://login.windows.net",