TT#61761 Use Django 1.11.17 to support Python 3.7

Otherwise building against Debian/buster with python 3.7 fails with:

|   File "/build/repoapi-0.3.0+0~20190702124241.289+buster~1.gbp167a8a/venv_prod/lib/python3.7/site-packages/django/contrib/admin/widgets.py", line 151
|     '%s=%s' % (k, v) for k, v in params.items(),
|     ^
| SyntaxError: Generator expression must be parenthesized

The underlying issue is #32012 in python (see
https://bugs.python.org/issue32012), which disallows ambiguous syntax
f(x for x in [1],), which is fixed only with Django >=1.11.17, see
931c60c521

Quoting from https://docs.djangoproject.com/en/dev/faq/install/#what-python-version-can-i-use-with-django:

| Django version | Python versions
+----------------+-------------------------------------------
| 1.11           | 2.7, 3.4, 3.5, 3.6, 3.7 (added in 1.11.17)
| 2.0            | 3.4, 3.5, 3.6, 3.7
| 2.1, 2.2       | 3.5, 3.6, 3.7
| 3.0            | 3.6, 3.7, 3.8

Change-Id: I4a1db7488792e5374c0f82629dfcfba0a6419be5

requirements/common.txt

@@ -1,4 +1,4 @@
-Django==1.11
+Django==1.11.17
 django-extensions
 yuicompressor
 django-assets