spawn: update submodule

pulls in fixes for exception handling, and support for multiple return
values with std::tuple<>

Signed-off-by: Casey Bodley <cbodley@redhat.com>

diff --git a/src/spawn b/src/spawn
index 5f4742f647a5a33b9467f648a3968b3cd0a681ee..9ee6d12f35ab2fa48b469f13b4830a5e5cfde45e 160000 (submodule)
--- a/src/spawn
+++ b/src/spawn
@@ -1 +1 @@
-Subproject commit 5f4742f647a5a33b9467f648a3968b3cd0a681ee
+Subproject commit 9ee6d12f35ab2fa48b469f13b4830a5e5cfde45e