bump MSRV to 1.40.0

Author: Be-ing

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
       fail-fast: false
       matrix:
         rust:
-          - 1.30.0
+          - 1.40.0
           - stable
           - beta
           - nightly

Cargo.toml

@@ -12,6 +12,7 @@ A library to run the pkg-config system tool at build time in order to be used in
 Cargo build scripts.
 """
 keywords = ["build-dependencies"]
+rust-version = "1.40"
 
 [dev-dependencies]
 lazy_static = "1"

README.md

@@ -13,7 +13,7 @@ You can use this crate directly to probe for specific libraries, or use
 [system-deps](https://github.com/gdesmott/system-deps) to declare all your
 `pkg-config` dependencies in `Cargo.toml`.
 
-This library requires Rust 1.30+.
+This library requires Rust 1.40+.
 
 # Example