[deps] Dropped Django 1.11 and Python 3.5

Django 1.11 is EOL since April 1, 2020.
Python 3.5 is going to be EOL on September 13, 2020,
let's anticipate that a bit in order to make our life easier.

.travis.yml

@@ -1,36 +1,37 @@
-dist: xenial
+dist: focal
 language: python
 cache: pip
+
 addons:
-  postgresql: "9.4"
+  postgresql: "12"
   apt:
     packages:
-      - postgresql-9.4-postgis-2.4
+      - postgresql-12-postgis-3
 services:
   - postgresql
 
 matrix:
   include:
-    - { python: "3.5", env: TOXENV=py35-django111 }
-    - { python: "3.6", env: TOXENV=py36-django111 }
-    - { python: "3.5", env: TOXENV=py35-django21 }
     - { python: "3.6", env: TOXENV=py36-django21 }
     - { python: "3.7", env: TOXENV=py37-django21 }
-    - { python: "3.5", env: TOXENV=py35-django22 }
     - { python: "3.6", env: TOXENV=py36-django22 }
     - { python: "3.7", env: TOXENV=py37-django22 }
     - { python: "3.6", env: TOXENV=py36-django30 }
     - { python: "3.7", env: TOXENV=py37-django30 }
-    - { python: "3.8-dev", env: TOXENV=py38-django30 }
-
+    - { python: "3.6", env: TOXENV=py36-django31 }
+    - { python: "3.7", env: TOXENV=py37-django31 }
+    - { python: "3.8", env: TOXENV=py38-django30 }
+    - { python: "3.8", env: TOXENV=py38-django31 }
 
 branches:
   only:
     - master
+
 before_install:
   - sudo add-apt-repository ppa:ubuntugis/ubuntugis-unstable -y
   - sudo apt-get update -q
   - sudo apt-get install binutils libproj-dev gdal-bin -y
+
 install:
   - pip install tox
   - pip install docutils pygments  # for setup.py check -r -s

README.rst

@@ -39,6 +39,7 @@ Compatibility with DRF, Django and Python
 
 ===============  ============================ ==================== ==================================
 DRF-gis version  DRF version                  Django version       Python version
+**0.16.x**       **3.10**                     **2.2 to 3.1**       **3.6** to **3.8**
 **0.15.x**       **3.10**                     **1.11, 2.2 to 3.0** **3.5** to **3.8**
 **0.14.x**       **3.3** to **3.9**           **1.11** to **2.1**   **3.4** to **3.7**
 **0.13.x**       **3.3** to **3.8**           **1.11** to **2.0**   **2.7** to **3.6**

tox.ini

@@ -1,7 +1,6 @@
 [tox]
 envlist =
-    py{35,36,py3}-django111{,-pytest}
-    py{35,36,37,py3}-django{21, 22}{,-pytest}
+    py{36,37,py3}-django{21, 22}{,-pytest}
     py{36,37,38,py3}-django{30, 31}{,-pytest}
 
 [testenv]
@@ -18,7 +17,6 @@ commands =
     travis: - coveralls
 
 deps =
-    django111: Django~=1.11
     django22: Django~=2.2
     django30: Django~=3.0
     django31: Django~=3.1