fix: de/normalise all file separators in a string

currently our tests fail on Windows because we neglect to normalise/denormalise all path separators.
when interacting with the local filesystem, we need to make sure to use the native separator (slash on linux, backslash on windows).
our normalising function used `string.prototype.replace(str, str)` which replaces only the first occurrence in a string.
this commit fixes it to the `string.prototype.replace(regex, str)` signature which, coupled with a global regex, replaces all occurences.

this commit isn't accompanied with a test since an existing test is already broken, and that test passing will be the proof of correctness.

lib/module-utils.js

@@ -39,14 +39,14 @@ function normalizeScriptPath(scriptPath) {
 
 function normaliseSeparator(pathToNormalise) {
   if (path.sep === '\\') {
-    return pathToNormalise.replace('/', '\\');
+    return pathToNormalise.replace(/\//g, '\\');
   }
   return pathToNormalise;
 }
 
 function denormaliseSeparator(pathToDenormalise) {
   if (path.sep === '\\') {
-    return pathToDenormalise.replace('\\', '/');
+    return pathToDenormalise.replace(/\\/g, '/');
   }
   return pathToDenormalise;
 }