Dropped support for GCC 5.

.travis.yml

@@ -14,16 +14,6 @@ addons:
       - re2c
 matrix:
   include:
-    - env: COMPILER_NAME=g++ _CXX=g++-5 _CC=gcc-5
-      os: linux
-      language: cpp
-      addons:
-        apt:
-          sources:
-            - *default_sources
-          packages:
-            - *default_packages
-            - g++-5
     - env: COMPILER_NAME=g++ _CXX=g++-6 _CC=gcc-6
       os: linux
       language: cpp

README.md

@@ -15,7 +15,7 @@ $ anthem [options] file...
 ## Building
 
 `anthem` requires [CMake](https://cmake.org/) and [Boost](http://www.boost.org/) for building.
-After installing the dependencies, `anthem` is built with a C++14 compiler (preferrably GCC ≥ 6.1 or clang ≥ 3.8).
+After installing the dependencies, `anthem` is built with a C++14 compiler (GCC ≥ 6.1 or clang ≥ 3.8).
 
 ```bash
 $ git clone https://github.com/potassco/anthem.git