Don't require a revision to import govendor config

There are valid govendor configs in the wild that do not have a revision
set, essentially requiring the package but not locking to a revision. We
should allow that and not stop the import.

internal/importers/govendor/importer.go

@@ -101,11 +101,8 @@ func (g *Importer) convert(pr gps.ProjectRoot) (*dep.Manifest, *dep.Lock, error)
 			return nil, nil, err
 		}
 
-		// Revision must not be empty
-		if pkg.Revision == "" {
-			err := errors.New("invalid govendor configuration, Revision is required")
-			return nil, nil, err
-		}
+		// There are valid govendor configs in the wild that don't have a revision set
+		// so we are not requiring it to be set during import
 
 		ip := base.ImportedPackage{
 			Name:     pkg.Path,

internal/importers/govendor/importer_test.go

@@ -124,7 +124,7 @@ func TestGovendorConfig_Convert(t *testing.T) {
 				WantConvertErr: true,
 			},
 		},
-		"missing package revision": {
+		"missing package revision doesn't cause an error": {
 			govendorFile{
 				Package: []*govendorPackage{
 					{
@@ -133,7 +133,7 @@ func TestGovendorConfig_Convert(t *testing.T) {
 				},
 			},
 			importertest.TestCase{
-				WantConvertErr: true,
+				WantConstraint: "*",
 			},
 		},
 	}