Test against Django 1.8b1

Signed-off-by: Michal Čihař <michal@cihar.com>

.travis.yml

@@ -17,7 +17,7 @@ env:
     - CI_DJANGO="Django>=1.7,<1.8" CI_DATABASE=mysql
     - CI_DJANGO="Django>=1.7,<1.8" CI_DATABASE=postgresql
     - CI_DJANGO="Django>=1.7,<1.8"
-    - CI_DJANGO="https://www.djangoproject.com/download/1.8a1/tarball/"
+    - CI_DJANGO="https://www.djangoproject.com/download/1.8b1/tarball/"
     - CI_DJANGO="Django>=1.7,<1.8" CI_DATABASE=postgresql CI_RUN_TESTS="-p test_selenium.py" CI_SELENIUM=1
     - CI_DJANGO="https://github.com/django/django/zipball/master"
   global: