Update Cargo.toml to in-tree version

Change-Id: I0acac0e9d2d547363954f67b6e7bed3de0ddb2a3
diff --git a/Cargo.toml b/Cargo.toml
index 729238d..d2cd657 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -29,7 +29,7 @@
 mio = "0.6.10"
 
 [target.'cfg(target_os = "fuchsia")'.dependencies]
-fuchsia-zircon = "0.3.2"
+fuchsia-zircon = { path = "../../../garnet/public/rust/crates/fuchsia-zircon" }
 libc = "0.2.34"
 net2 = "0.2.29"