bump to rust 1.31.1

Author: pietroalbini

src/bootstrap/channel.rs

@@ -24,7 +24,7 @@ use Build;
 use config::Config;
 
 // The version number
-pub const CFG_RELEASE_NUM: &str = "1.31.0";
+pub const CFG_RELEASE_NUM: &str = "1.31.1";
 
 pub struct GitInfo {
     inner: Option<Info>,