title: Travis-CI allow_failures when multiple environment variables are set
body: <p>I'm trying to set <code>allow_failures</code> for a complex build process, but unfortunately it isn't working.</p>
  
  <p>The problem is that in my <code>env</code> I am setting multiple environment variables, and cannot get Travis to recognise that I want on of these rows to be allowed to fail.</p>
  
  <p><a href="https://docs.travis-ci.com/user/customizing-the-build#Rows-that-are-Allowed-to-Fail" rel="nofollow">The documentation on <code>allow_failures</code></a> shows how to allow a single <code>env</code> to fail, along with another configuration option, but doesn't cover how to allow a multiple enviroment variable setup to fail.</p>
  
  <p>The troublesome sections of the <code>.travis.yml</code> file are below:</p>
  
  <pre><code>env:
    - DJANGO_VERSION='1.8,&lt;1.9' DB=sqlitefile   SEARCH=whoosh
    - DJANGO_VERSION='1.8,&lt;1.9' DB=postgres     SEARCH=whoosh
    - DJANGO_VERSION='1.8,&lt;1.9' DB=mysql        SEARCH=whoosh
    - DJANGO_VERSION='1.8,&lt;1.9' DB=sqlitefile   SEARCH=elasticsearch
    - DJANGO_VERSION='1.8,&lt;1.9' DB=postgres     SEARCH=elasticsearch
    - DJANGO_VERSION='1.8,&lt;1.9' DB=mysql        SEARCH=elasticsearch
  
  matrix:
    allow_failures:
      - env: DJANGO_VERSION='1.8,&lt;1.9'  DB=mysql  SEARCH=elasticsearch
      - env: DJANGO_VERSION='1.8,&lt;1.9'  DB=mysql  SEARCH=whoosh
  </code></pre>
  
  <p>How can I do this?</p>