chore: update internal Node.js function call

This updates the call to `_resolveLookupPaths`. It returns a string
by default since Node.js v8 when called with a third truthy argument.
The backwards compatible return value should change soon, so detect
what return type is used and handle both cases.

src/util.js

@@ -98,8 +98,10 @@ function packageNameFromPath(path) {
  */
 function findModulePath(request, parent) {
   var mainScriptDir = path.dirname(Module._resolveFilename(request, parent));
-  var resolvedModule = Module._resolveLookupPaths(request, parent);
-  var paths = resolvedModule[1];
+  var resolvedModule = Module._resolveLookupPaths(request, parent, true);
+  var paths = typeof resolvedModule === 'string' || resolvedModule === null ?
+    resolvedModule :
+    resolvedModule[1];
   for (var i = 0, PL = paths.length; i < PL; i++) {
     if (mainScriptDir.indexOf(paths[i]) === 0) {
       return path.join(paths[i], request.replace('/', path.sep));