Adjust requirements for Django 1.8.

requirements.txt

-django>=1.4, <1.5
+django>=1.8, <1.9
 pyyaml
--e git+https://github.com/edx/XBlock.git@tag-master-2015-05-22#egg=XBlock
--e git+https://github.com/edx/xblock-utils.git@b4f9b51146c7fafa12f41d54af752b8f1516dffd#egg=xblock-utils
--e .
+git+https://github.com/edx/XBlock.git@xblock-0.4.2#egg=XBlock
+git+https://github.com/edx/xblock-utils.git@v1.0.0#egg=xblock-utils
+.

test-requirements.txt

 -r requirements.txt
 
--e git+https://github.com/edx/xblock-sdk.git@629650ed6fc1b77d1a5287debeace0b29db7c0fd#egg=xblock-sdk
+-e git+https://github.com/edx/xblock-sdk.git@4e8e713e7dd886b8d2eb66b5001216b66b9af81a#egg=xblock-sdk
 
 ddt
 selenium==2.48.0