Update go.mod and Prometheus version

Updates various internal dependencies in go.mod, and Prometheus
within docker-compose.yaml

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

vendor/golang.org/x/sys/unix/unveil_openbsd.go

@@ -4,39 +4,48 @@
 
 package unix
 
-import (
-	"syscall"
-	"unsafe"
-)
+import "fmt"
 
 // Unveil implements the unveil syscall.
 // For more information see unveil(2).
 // Note that the special case of blocking further
 // unveil calls is handled by UnveilBlock.
 func Unveil(path string, flags string) error {
-	pathPtr, err := syscall.BytePtrFromString(path)
+	if err := supportsUnveil(); err != nil {
+		return err
+	}
+	pathPtr, err := BytePtrFromString(path)
 	if err != nil {
 		return err
 	}
-	flagsPtr, err := syscall.BytePtrFromString(flags)
+	flagsPtr, err := BytePtrFromString(flags)
 	if err != nil {
 		return err
 	}
-	_, _, e := syscall.Syscall(SYS_UNVEIL, uintptr(unsafe.Pointer(pathPtr)), uintptr(unsafe.Pointer(flagsPtr)), 0)
-	if e != 0 {
-		return e
-	}
-	return nil
+	return unveil(pathPtr, flagsPtr)
 }
 
 // UnveilBlock blocks future unveil calls.
 // For more information see unveil(2).
 func UnveilBlock() error {
-	// Both pointers must be nil.
-	var pathUnsafe, flagsUnsafe unsafe.Pointer
-	_, _, e := syscall.Syscall(SYS_UNVEIL, uintptr(pathUnsafe), uintptr(flagsUnsafe), 0)
-	if e != 0 {
-		return e
+	if err := supportsUnveil(); err != nil {
+		return err
 	}
+	return unveil(nil, nil)
+}
+
+// supportsUnveil checks for availability of the unveil(2) system call based
+// on the running OpenBSD version.
+func supportsUnveil() error {
+	maj, min, err := majmin()
+	if err != nil {
+		return err
+	}
+
+	// unveil is not available before 6.4
+	if maj < 6 || (maj == 6 && min <= 3) {
+		return fmt.Errorf("cannot call Unveil on OpenBSD %d.%d", maj, min)
+	}
+
 	return nil
 }