Bump to mono/2017-04/1a227379 (#624)

jonpryor · web-flow · commit 84d4230d1395 · 2017-06-01T16:13:09.000-04:00
Fixes: https://bugzilla.xamarin.com/show_bug.cgi?id=56874
diff --git a/external/mono b/external/mono
@@ -1 +1 @@
-Subproject commit 8d1f89f0834ba8a3943c2eb8d0447ba8f500cd37
+Subproject commit 1a227379203671064ef08aa062af5e5c606d0ec9
