Update vendoring

vendor/github.com/docker/cli/opts/env.go

@@ -0,0 +1,46 @@
+package opts
+
+import (
+	"fmt"
+	"os"
+	"runtime"
+	"strings"
+)
+
+// ValidateEnv validates an environment variable and returns it.
+// If no value is specified, it returns the current value using os.Getenv.
+//
+// As on ParseEnvFile and related to #16585, environment variable names
+// are not validate what so ever, it's up to application inside docker
+// to validate them or not.
+//
+// The only validation here is to check if name is empty, per #25099
+func ValidateEnv(val string) (string, error) {
+	arr := strings.Split(val, "=")
+	if arr[0] == "" {
+		return "", fmt.Errorf("invalid environment variable: %s", val)
+	}
+	if len(arr) > 1 {
+		return val, nil
+	}
+	if !doesEnvExist(val) {
+		return val, nil
+	}
+	return fmt.Sprintf("%s=%s", val, os.Getenv(val)), nil
+}
+
+func doesEnvExist(name string) bool {
+	for _, entry := range os.Environ() {
+		parts := strings.SplitN(entry, "=", 2)
+		if runtime.GOOS == "windows" {
+			// Environment variable are case-insensitive on Windows. PaTh, path and PATH are equivalent.
+			if strings.EqualFold(parts[0], name) {
+				return true
+			}
+		}
+		if parts[0] == name {
+			return true
+		}
+	}
+	return false
+}