[vpython] Fix PEP425 naming.

vpython/spec/spec.go

 // Copyright 2017 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package spec
 
 import (
         "crypto/sha256"
         "encoding/hex"
         "fmt"
@@ skipping 84 matching lines @@
 func (s specPackageSlice) Len() int      { return len(s) }
 func (s specPackageSlice) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
 
 func (s specPackageSlice) Less(i, j int) bool {
         return sortby.Chain{
                 func(i, j int) bool { return s[i].Name < s[j].Name },
                 func(i, j int) bool { return s[i].Version < s[j].Version },
         }.Use(i, j)
 }
 
-type pep425TagSlice []*vpython.Pep425Tag
+type pep425TagSlice []*vpython.PEP425Tag
 
 func (s pep425TagSlice) Len() int      { return len(s) }
 func (s pep425TagSlice) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
 
 func (s pep425TagSlice) Less(i, j int) bool {
         return sortby.Chain{
-                func(i, j int) bool { return s[i].Version < s[j].Version },
+                func(i, j int) bool { return s[i].Python < s[j].Python },
                 func(i, j int) bool { return s[i].Abi < s[j].Abi },
-                func(i, j int) bool { return s[i].Arch < s[j].Arch },
+                func(i, j int) bool { return s[i].Platform < s[j].Platform },
         }.Use(i, j)
 }