[vpython] Fix PEP425 naming.

vpython/cipd/pep425_test.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 cipd
 
 import (
         "fmt"
         "testing"
 
         "github.com/luci/luci-go/vpython/api/vpython"
 
         . "github.com/smartystreets/goconvey/convey"
 )
 
-func mkTag(arch string) *vpython.Pep425Tag {
-        return &vpython.Pep425Tag{
-                Version: "cp27",
-                Abi:     "none",
-                Arch:    arch,
+func mkTag(plat string) *vpython.PEP425Tag {
+        return &vpython.PEP425Tag{
+                Python:   "cp27",
+                Abi:      "none",
+                Platform: plat,
         }
 }
 
 func TestPlatformForPEP425Tag(t *testing.T) {
         t.Parallel()
 
         testCases := []struct {
-                tag      *vpython.Pep425Tag
+                tag      *vpython.PEP425Tag
                 platform string
         }{
                 {mkTag("junk_i686"), ""},
 
                 {mkTag("linux_sparc64"), ""},
                 {mkTag("linux_i686"), "linux-386"},
                 {mkTag("manylinux1_i686"), "linux-386"},
                 {mkTag("linux_x86_64"), "linux-amd64"},
                 {mkTag("manylinux1_x86_64"), "linux-amd64"},
                 {mkTag("linux_arm64"), "linux-arm64"},
@@ skipping 14 matching lines @@
         }
 
         Convey(`Testing PEP425 tag selection`, t, func() {
                 for _, tc := range testCases {
                         Convey(fmt.Sprintf("Tag %q => %q", tc.tag.TagString(), tc.platform), func() {
                                 So(PlatformForPEP425Tag(tc.tag), ShouldResemble, tc.platform)
                         })
                 }
         })
 }