chore(dependencies): Bump spmc, since 0.2 was yanked

Author: alex

Cargo.toml

@@ -51,7 +51,7 @@ want = { git = "https://github.com/seanmonstar/want", branch = "std-future" }
 matches = "0.1"
 num_cpus = "1.0"
 pretty_env_logger = "0.3"
-spmc = "0.2"
+spmc = "0.3"
 serde = "1.0"
 serde_derive = "1.0"
 serde_json = "1.0"