Update the minimal Rust version

.travis.yml

@@ -2,12 +2,13 @@ language: rust
 dist: xenial
 
 rust:
-    - "1.32.0"
-    - "1.33.0"
     - "1.34.2"
     - "1.35.0"
     - "1.36.0"
     - "1.37.0"
+    - "1.38.0"
+    - "1.39.0"
+    - "1.40.0"
     - "stable"
     - "beta"
     - "nightly"

README.md

@@ -58,7 +58,7 @@ This project provides the following man pages:
 
 ## Build from source
 
-In order to compile ADMEd, you will need the [Rust](https://www.rust-lang.org/) compiler and its package manager, Cargo. The minimal required Rust version is 1.32.0, although it is recommended to use the latest stable one.
+In order to compile ACMEd, you will need the [Rust](https://www.rust-lang.org/) compiler and its package manager, Cargo. The minimal required Rust version is 1.34.2, although it is recommended to use the latest stable one.
 
 ACMEd depends OpenSSL 1.1.0 or higher.