Issue with installing Django.

[omps]

Downloading Django-2.0.tar.gz (8.0MB)
100% |████████████████████████████████| 8.0MB 103kB/s
Complete output from command python setup.py egg_info:
Traceback (most recent call last):
File "", line 1, in
File "/tmp/pip-build-qItdzL/django/setup.py", line 32, in
version = import('django').get_version()
File "django/init.py", line 1, in
from django.utils.version import get_version
File "django/utils/version.py", line 61, in
@functools.lru_cache()
AttributeError: 'module' object has no attribute 'lru_cache'

[omps]

https://stackoverflow.com/questions/42196124/there-are-errors-when-i-install-django-by-git

The last Django version does not support python 2.7.If you really want to use python 2.7 and also use Django you should install a previous Django version.The latest supported is: 1.11Therefore, just run:

pip install django==1.11

@ldoktor Version no. need to be updated in the avocado-server documentation.

[omps]

submitter PR #58