[travis] also test on python 2.7.6

We install python 2.7.6 using pyenv.

This should help us catch issues like this earlier
https://github.com/fonttools/fonttools/issues/993

.travis.yml

@@ -26,6 +26,19 @@ matrix:
       env:
         - TOXENV=py35-cov
         - HOMEBREW_NO_AUTO_UPDATE=1
+    - env:
+        - TOXENV=py27-cov
+        - PYENV_VERSION='2.7.6'
+        - PYENV_VERSION_STRING='Python 2.7.6'
+        - TRAVIS_PYENV_VERSION='0.4.0'
+
+cache:
+  - pip
+  - directories:
+    - $HOME/.pyenv_cache
+
+before_install:
+  - source ./.travis/before_install.sh
 
 install:
   - ./.travis/install.sh

.travis/before_install.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+set -e
+set -x
+
+if [[ -n "$PYENV_VERSION" ]]; then
+    wget https://github.com/praekeltfoundation/travis-pyenv/releases/download/${TRAVIS_PYENV_VERSION}/setup-pyenv.sh
+    source setup-pyenv.sh
+fi