[gnome-builder] Update Rust snippets

[Christian Hergert <chergert src gnome org>]

commit 542d36c14d6684cf847dde9569ce25eb2deadedb
Author: Ricardo Silva Veloso <ricvelozo gmail com>
Date:   Fri Dec 27 21:13:15 2019 -0300

    Update Rust snippets

 src/plugins/snippets/snippets/rust.snippets | 7 +++++++
 1 file changed, 7 insertions(+)
---
diff --git a/src/plugins/snippets/snippets/rust.snippets b/src/plugins/snippets/snippets/rust.snippets
index f1ffd75d0..f166d59b3 100644
--- a/src/plugins/snippets/snippets/rust.snippets
+++ b/src/plugins/snippets/snippets/rust.snippets
@@ -70,6 +70,10 @@ snippet no_main
 - desc #![no_main]
        #![no_main]
        $0
+snippet non_exhaustive
+- desc #[non_exhaustive]
+       #[non_exhaustive]
+       $0
 snippet inline
 - desc #[inline]
        #[inline]
@@ -277,6 +281,9 @@ snippet unreachable
 snippet unimplemented
 - desc unimplemented!()
        unimplemented!()$0
+snippet todo
+- desc todo!()
+       todo!()$0
 snippet assert
 - desc assert!(…)
        assert!(${1:expression})$0