fix: don't enable default features in tower (#972)

Author: Noah-Kennedy

tonic/Cargo.toml

@@ -79,7 +79,7 @@ hyper = {version = "0.14.14", features = ["full"], optional = true}
 hyper-timeout = {version = "0.4", optional = true}
 tokio = {version = "1.0.1", features = ["net"], optional = true}
 tokio-stream = "0.1"
-tower = {version = "0.4.7", features = ["balance", "buffer", "discover", "limit", "load", "make", "timeout", "util"], optional = true}
+tower = {version = "0.4.7", default-features = false, features = ["balance", "buffer", "discover", "limit", "load", "make", "timeout", "util"], optional = true}
 tracing-futures = {version = "0.2", optional = true}
 axum = {version = "0.5", default_features = false, optional = true}