removed useless pragma

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name           = "prometheus_exporter_base"
-version        = "0.30.1"
+version        = "0.30.2"
 authors        = ["Francesco Cogno <francesco.cogno@outlook.com>"]
 edition        = "2018"
 description    = "Prometheus Rust exporters base crate with boilerplate"

README.md

@@ -10,9 +10,9 @@ master | dev |
 
 [![Crate](https://img.shields.io/crates/v/prometheus_exporter_base.svg)](https://crates.io/crates/prometheus_exporter_base) [![cratedown](https://img.shields.io/crates/d/prometheus_exporter_base.svg)](https://crates.io/crates/prometheus_exporter_base) [![cratelastdown](https://img.shields.io/crates/dv/prometheus_exporter_base.svg)](https://crates.io/crates/prometheus_exporter_base)
 
-[![release](https://img.shields.io/github/release/MindFlavor/prometheus_exporter_base.svg)](https://github.com/MindFlavor/prometheus_exporter_base/tree/0.30.1)
-[![tag](https://img.shields.io/github/tag/mindflavor/prometheus_exporter_base.svg)](https://github.com/MindFlavor/prometheus_exporter_base/tree/0.30.1)
-[![commitssince](https://img.shields.io/github/commits-since/mindflavor/prometheus_exporter_base/0.30.1.svg)](https://img.shields.io/github/commits-since/mindflavor/prometheus_exporter_base/0.30.1.svg)
+[![release](https://img.shields.io/github/release/MindFlavor/prometheus_exporter_base.svg)](https://github.com/MindFlavor/prometheus_exporter_base/tree/0.30.2)
+[![tag](https://img.shields.io/github/tag/mindflavor/prometheus_exporter_base.svg)](https://github.com/MindFlavor/prometheus_exporter_base/tree/0.30.2)
+[![commitssince](https://img.shields.io/github/commits-since/mindflavor/prometheus_exporter_base/0.30.2.svg)](https://img.shields.io/github/commits-since/mindflavor/prometheus_exporter_base/0.30.2.svg)
 
 ## Goal
 

src/lib.rs

@@ -1,4 +1,3 @@
-#![feature(async_closure)]
 extern crate failure;
 extern crate serde_json;
 use http::StatusCode;