Update .travis.yml references to DRF 3.0 were removed

Author: angvp-sng

.travis.yml

@@ -6,7 +6,6 @@ env:
     - TOX_ENV=py27-flake8
     - TOX_ENV=py27-docs
 
-    - TOX_ENV=py27-django1.8-drf3.0
     - TOX_ENV=py27-django1.8-drf3.1
     - TOX_ENV=py27-django1.8-drf3.2
     - TOX_ENV=py27-django1.8-drf3.3
@@ -19,13 +18,11 @@ env:
 
     - TOX_ENV=py27-django1.10-drf3.4
 
-    - TOX_ENV=py33-django1.8-drf3.0
     - TOX_ENV=py33-django1.8-drf3.1
     - TOX_ENV=py33-django1.8-drf3.2
     - TOX_ENV=py33-django1.8-drf3.3
     - TOX_ENV=py33-django1.8-drf3.4
 
-    - TOX_ENV=py34-django1.8-drf3.0
     - TOX_ENV=py34-django1.8-drf3.1
     - TOX_ENV=py34-django1.8-drf3.2
     - TOX_ENV=py34-django1.8-drf3.3