endpoints: Add Strava endpoint

As per the Strava API auth docs: http://developers.strava.com/docs/authentication/

Change-Id: Ibf6fcca193a1b63bf86830b669849653774a9df9
GitHub-Last-Rev: 296e91e1f2
GitHub-Pull-Request: golang/oauth2#473
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/289829
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Trust: Brad Fitzpatrick <bradfitz@golang.org>
Trust: Heschi Kreinick <heschi@google.com>

endpoints/endpoints.go

@@ -167,6 +167,12 @@ var StackOverflow = oauth2.Endpoint{
 	TokenURL: "https://stackoverflow.com/oauth/access_token",
 }
 
+// Strava is the endpoint for Strava.
+var Strava = oauth2.Endpoint{
+	AuthURL:  "https://www.strava.com/oauth/authorize",
+	TokenURL: "https://www.strava.com/oauth/token",
+}
+
 // Twitch is the endpoint for Twitch.
 var Twitch = oauth2.Endpoint{
 	AuthURL:  "https://id.twitch.tv/oauth2/authorize",