Update .gitmodules

Our other releases use incubator, let's see if this is causing
the issue in our CI.

Signed-off-by: Sophie Wigmore <swigmore@pivotal.io>

.gitmodules

@@ -1,6 +1,6 @@
 [submodule "src/code.cloudfoundry.org/windows2016fs"]
 	path = src/code.cloudfoundry.org/windows2016fs
-	url = https://github.com/cloudfoundry/windows2016fs
+	url = https://github.com/cloudfoundry-incubator/windows2016fs
 [submodule "src/code.cloudfoundry.org/hydrator"]
 	path = src/code.cloudfoundry.org/hydrator
 	url = https://github.com/cloudfoundry/hydrator