Update some witx Rust dependencies (#246)

Minor updates!

Author: alexcrichton

tools/witx/Cargo.toml

@@ -17,9 +17,9 @@ crate-type=["rlib"]
 anyhow = "1"
 log = "0.4"
 thiserror = "1.0"
-wast = { version = "9.0.0", default-features = false }
+wast = { version = "11.0.0", default-features = false }
 
 [dev-dependencies]
 diff = "0.1.11"
-pretty_env_logger = "0.3"
+pretty_env_logger = "0.4"
 structopt = "0.3"