[rust] Update Rust toolchain

Change-Id: Ib1a7bf30addc660b968639da8354b388a72f3aff
diff --git a/fuchsia.ensure b/fuchsia.ensure
index 9f45307..2eca179 100644
--- a/fuchsia.ensure
+++ b/fuchsia.ensure
@@ -45,7 +45,7 @@
 
 # Rust
 @Subdir rust
-fuchsia/rust/${platform} git_revision:7c98d2e63f732682b057c8c453b08f9e12b262e6
+fuchsia/rust/${platform} git_revision:81cfaad030435aae447d73c66123b3df856c09cb
 
 # Swift
 @Subdir swift