oauth2: fix some typos in code comments

Change-Id: I3bd85f097e30d693965541eac65df057288c2086
Reviewed-on: https://go-review.googlesource.com/73130
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

internal/token.go

@@ -20,7 +20,7 @@ import (
 	"golang.org/x/net/context/ctxhttp"
 )
 
-// Token represents the crendentials used to authorize
+// Token represents the credentials used to authorize
 // the requests to access protected resources on the OAuth 2.0
 // provider's backend.
 //

token.go

@@ -20,7 +20,7 @@ import (
 // expirations due to client-server time mismatches.
 const expiryDelta = 10 * time.Second
 
-// Token represents the crendentials used to authorize
+// Token represents the credentials used to authorize
 // the requests to access protected resources on the OAuth 2.0
 // provider's backend.
 //