Update to fuchsia-zircon 0.3

Change-Id: Ifbf3cd13e12a8c8bc651d9348da65e7214875c24
diff --git a/Cargo.toml b/Cargo.toml
index b04f290..40ba4e9 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -27,7 +27,7 @@
 futures = "0.1.15"
 
 [target.'cfg(target_os = "fuchsia")'.dependencies]
-fuchsia-zircon = "0.2"
+fuchsia-zircon = "0.3"
 
 [dev-dependencies]
 env_logger = { version = "0.4", default-features = false }