fix double requirement

.travis.yml

@@ -5,7 +5,5 @@ python:
   - "2.7"
 # command to run tests
 # script: nosetests
-env:
-  - DJANGO_VERSION=1.4.2
 install:
-  - pip install -r requirements.txt -q Django==$DJANGO_VERSION
+  - pip install -r .travis/requirements_1.4.txt

.travis/requirements.txt

+South
+Markdown<2.3.0
+django-sekizai<0.7
+django-mptt>=0.5.3
+sorl-thumbnail
+

.travis/requirements_1.4.txt

+-r requirements.txt
+Django>=1.4,<1.5