jira: fix bug when upper-casing scopes

Fix for a small bug that causes scopes to be prefixed by a bunch
of `+` chars, which results in an invalid scopes response from
the Jira Auth Server.

Change-Id: I00ded66c1eeb042a02f11ef3c84d7281159b1039
GitHub-Last-Rev: f76f48058979f4c7690b702a4fb31f245f9f7043
GitHub-Pull-Request: golang/oauth2#282
Reviewed-on: https://go-review.googlesource.com/110917
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/jira/jira.go b/jira/jira.go
index e8021e9..3441560 100644
--- a/jira/jira.go
+++ b/jira/jira.go
@@ -94,8 +94,8 @@
 	// Add scopes if they exist;  If not, it defaults to app scopes
 	if scopes := js.conf.Scopes; scopes != nil {
 		upperScopes := make([]string, len(scopes))
-		for _, k := range scopes {
-			upperScopes = append(upperScopes, strings.ToUpper(k))
+		for i, k := range scopes {
+			upperScopes[i] = strings.ToUpper(k)
 		}
 		v.Set("scope", strings.Join(upperScopes, "+"))
 	}