Add test that pulls dependencies from pylint and astroid @master

Travis CI is configured to run a cron job every day and this will
perform a decent job of notifying us when pylint or astroid change
something that breaks pylint-django.

Author: atodorov

.travis.yml

@@ -18,6 +18,7 @@ matrix:
     - { stage: django_is_installed, python: 3.6, env: TOXENV=django_is_installed }
     - { stage: test, python: 3.6, env: DJANGO=2.0 }
     - { stage: test, python: 3.6, env: DJANGO=1.11 }
+    - { stage: test, python: 3.6, env: DJANGO=master }
     - { stage: test, python: 3.6, env: TOXENV=flake8 }
     - { stage: test, python: 3.6, env: TOXENV=pylint }
     - { stage: test, python: 3.6, env: TOXENV=readme }

tox.ini

@@ -8,7 +8,7 @@ envlist =
     flake8
     pylint
     readme
-    py{36}-django{111,20}
+    py{36}-django{111,20,-master}
     py{35,36,37}-django21
 
 [testenv]
@@ -18,7 +18,7 @@ commands =
     flake8: flake8
     pylint: pylint --rcfile=tox.ini -d missing-docstring,too-many-branches,too-many-return-statements,too-many-ancestors,fixme --ignore=tests pylint_django setup
     readme: python setup.py check --restructuredtext --strict
-    py{36}-django{111,20}: coverage run pylint_django/tests/test_func.py -v
+    py{36}-django{111,20,-master}: coverage run pylint_django/tests/test_func.py -v
     py{35,36,37}-django21: coverage run pylint_django/tests/test_func.py -v
     clean: find . -type f -name '*.pyc' -delete
     clean: find . -type d -name __pycache__ -delete
@@ -27,11 +27,14 @@ deps =
     django_is_installed: Django
     flake8: flake8
     pylint: pylint
-    pylint: Django>=2.0,<2.1
+    pylint: Django
     readme: readme_renderer
     django111: Django>=1.11,<2.0
     django20: Django>=2.0,<2.1
     django21: Django>=2.1,<2.2
+    django-master: Django
+    django-master: git+https://github.com/pycqa/astroid@master
+    django-master: git+https://github.com/pycqa/pylint@master
     py{35,36,37}: coverage
     py{35,36,37}: djangorestframework
     py{35,36,37}: django-model-utils
@@ -53,6 +56,7 @@ DJANGO =
     1.11: django111
     2.0: django20
     2.1: django21
+    master: django-master
 
 [flake8]
 max-line-length = 120