pip install django-freshdesk uninstalls Django 1.7.0+

Changed the install_requires to 'Django>=1.5.0,<1.8' to avoid an issue with pip uninstalling Django 1.7.1 in favour of Django 1.6.8 when I added django-freshdesk to my requirements.

It appears that tests are already passing for Django 1.7 in Travis but if there are any problems in the field I'll open up an issue/PR
Merge pull request #2 from huxley/patch-1

pip install django-freshdesk uninstalls Django 1.7.0+