more robust: potentially a workaround for spurious HOL build problems seen by Larry Paulson;

--- a/src/HOL/ROOT	Sat Jul 28 16:30:58 2018 +0200
+++ b/src/HOL/ROOT	Sat Jul 28 16:49:53 2018 +0200
@@ -4,6 +4,7 @@
   description {*
     Classical Higher-order Logic.
   *}
+  options [strict_facts]
   theories
     Main (global)
     Complex_Main (global)