cmd/go/internal/modfetch: update expected errors in TestCodeRepo

Updates golang/go#25501.

Before:

--- FAIL: TestCodeRepo (20.13s)
    --- FAIL: TestCodeRepo/github.com_rsc_vgotest1_v2/v2.0.0 (0.47s)
        coderepo_test.go:424: repo.Zip("v2.0.0"): missing or invalid go.mod, want error "missing go.mod"
    --- FAIL: TestCodeRepo/github.com_rsc_vgotest1_v2/80d85 (0.34s)
        coderepo_test.go:409: repo.GoMod("v2.0.0-20180219231006-80d85c5d4d17"): missing or invalid go.mod, want "missing go.mod"
        coderepo_test.go:424: repo.Zip("v2.0.0-20180219231006-80d85c5d4d17"): missing or invalid go.mod, want error "missing go.mod"
    --- FAIL: TestCodeRepo/github.com_rsc_vgotest1_v54321/80d85 (0.28s)
        coderepo_test.go:424: repo.Zip("v54321.0.0-20180219231006-80d85c5d4d17"): missing or invalid go.mod, want error "missing go.mod"
vgo: lookup code.google.com/p/go-uuid/uuid: unknown module code.google.com/p/go-uuid/uuid: no go-import tags

After:

ok      golang.org/x/vgo/vendor/cmd/go/internal/modfetch        123.433s

Change-Id: I1263af1104b36b519ab9e79c74bb8c2eed05797e
Reviewed-on: https://go-review.googlesource.com/119075
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>
diff --git a/vendor/cmd/go/internal/modfetch/coderepo_test.go b/vendor/cmd/go/internal/modfetch/coderepo_test.go
index 999e6b3..4a622e3 100644
--- a/vendor/cmd/go/internal/modfetch/coderepo_test.go
+++ b/vendor/cmd/go/internal/modfetch/coderepo_test.go
@@ -86,7 +86,7 @@
 		name:    "80d85c5d4d17598a0e9055e7c175a32b415d6128",
 		short:   "80d85c5d4d17",
 		time:    time.Date(2018, 2, 19, 23, 10, 6, 0, time.UTC),
-		ziperr:  "missing go.mod",
+		ziperr:  "missing or invalid go.mod",
 	},
 	{
 		path:    "github.com/rsc/vgotest1",
@@ -121,8 +121,8 @@
 		name:     "80d85c5d4d17598a0e9055e7c175a32b415d6128",
 		short:    "80d85c5d4d17",
 		time:     time.Date(2018, 2, 19, 23, 10, 6, 0, time.UTC),
-		gomoderr: "missing go.mod",
-		ziperr:   "missing go.mod",
+		gomoderr: "missing or invalid go.mod",
+		ziperr:   "missing or invalid go.mod",
 	},
 	{
 		path:    "github.com/rsc/vgotest1/v54321",
@@ -131,7 +131,7 @@
 		name:    "80d85c5d4d17598a0e9055e7c175a32b415d6128",
 		short:   "80d85c5d4d17",
 		time:    time.Date(2018, 2, 19, 23, 10, 6, 0, time.UTC),
-		ziperr:  "missing go.mod",
+		ziperr:  "missing or invalid go.mod",
 	},
 	{
 		path: "github.com/rsc/vgotest1/submod",
@@ -528,7 +528,7 @@
 	},
 	{
 		path:     "gopkg.in/natefinch/lumberjack.v2",
-		versions: []string{},
+		versions: nil,
 	},
 }