bootstrap: use file URL instead of relative url

Author: watilde

lib/internal/bootstrap/pre_execution.js

@@ -362,7 +362,7 @@ function initializePolicy() {
     // no bare specifiers for now
     let manifestURL;
     if (require('path').isAbsolute(experimentalPolicy)) {
-      manifestURL = new URL(experimentalPolicy, 'file://');
+      manifestURL = new URL(`file://${experimentalPolicy}`);
     } else {
       const cwdURL = pathToFileURL(process.cwd());
       cwdURL.pathname += '/';