Ensure cleanup executes for scripts-whitespace-windows test.

Test failure was leaving an assortment of files dangling around:
   test/tap/scripts-whitespace-windows/cache/scripts-whitespace-windows-dep/0.0.1/package.tgz
   test/tap/scripts-whitespace-windows/cache/scripts-whitespace-windows-dep/0.0.1/package/package.json

test/tap/scripts-whitespace-windows.js

@@ -31,7 +31,7 @@ test('setup', function (t) {
 
   child.stdout.setEncoding('utf8')
   child.stderr.on('data', function(chunk) {
-    throw new Error('got stderr data: ' + JSON.stringify('' + chunk))
+    t.fail('got stderr data: ' + JSON.stringify('' + chunk))
   })
   child.on('close', function () {
     t.end()
@@ -47,7 +47,7 @@ test('test', function (t) {
 
   child.stdout.setEncoding('utf8')
   child.stderr.on('data', function(chunk) {
-    throw new Error('got stderr data: ' + JSON.stringify('' + chunk))
+    t.fail('got stderr data: ' + JSON.stringify('' + chunk))
   })
   child.stdout.on('data', ondata)
   child.on('close', onend)