update rust minimum version to 1.27.0 (includes testing)

.travis.yml

@@ -2,6 +2,9 @@ language: rust
 matrix:
   fast_finish: true
   include:
+    - rust: 1.27.0
+      os: linux
+      env: FEATURES=''
     - rust: stable
       os: linux
       env: FEATURES=''
@@ -64,4 +67,3 @@ after_success: |
     cargo tarpaulin --out Xml
     bash <(curl -s https://codecov.io/bash)
   fi
-

README.md

@@ -36,7 +36,7 @@ Requirements
 ### Rust Version ###
 
 uutils follows Rust's release channels and is tested against stable, beta and nightly.
-The current oldest supported version of the Rust compiler is `1.22.0`.
+The current oldest supported version of the Rust compiler is `1.27.0`.
 
 On both Windows and Redox, only the nightly version is tested currently.