Update the minimal rustc version

.travis.yml

@@ -1,7 +1,7 @@
 language: rust
 
 rust:
-    - "1.31.0"
+    - "1.32.0"
     - "stable"
     - "beta"
     - "nightly"

README.md

@@ -27,7 +27,7 @@ The Automatic Certificate Management Environment (ACME), is an internet standard
 
 ## 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 1.31.0, although it is recommended to use the latest stable one.
+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.
 
 ACMEd depends on the OpenSSL. The minimal supported versions are those from the [openssl](https://docs.rs/openssl/) crate, currently OpenSSL 1.0.1 through 1.1.1 and LibreSSL 2.5 through 2.8.