fix(deps): move async-attributes over to dev-dependencies

Cargo.toml

@@ -11,7 +11,6 @@ readme = "README.md"
 categories = ["caching", "filesystem"]
 
 [dependencies]
-async-attributes = { version = "1.1.2", optional = true }
 async-std = { version = "1.10.0", features = ["unstable"], optional = true }
 digest = "0.10.6"
 either = "1.6.1"
@@ -38,6 +37,7 @@ tokio-stream = { version = "0.1.7", features = ["io-util"], optional = true }
 walkdir = "2.3.2"
 
 [dev-dependencies]
+async-attributes = { version = "1.1.2" }
 criterion = "0.4.0"
 lazy_static = "1.4.0"
 tokio = { version = "1.12.0", features = [
@@ -53,6 +53,6 @@ name = "benchmarks"
 harness = false
 
 [features]
-default = ["async-std", "async-attributes"]
+default = ["async-std"]
 link_to = []
 tokio-runtime = ["tokio", "tokio-stream"]