fix travis tests: explicitly install pyenv version

Also updates from 3.6 to 3.7

Author: crucialfelix

.travis.yml

@@ -1,20 +1,26 @@
 language: python
+cache:
+  directories:
+    - $HOME/.cache/pip
+    - /opt/python
 sudo: false
 env:
   - TOX_ENV=py27-flake8
-  - TOX_ENV=py36-flake8
+  - TOX_ENV=py37-flake8
   - TOX_ENV=py27-dj18
   - TOX_ENV=py27-dj19
   - TOX_ENV=py27-dj110
   - TOX_ENV=py27-dj111
-  - TOX_ENV=py36-dj18
-  - TOX_ENV=py36-dj19
-  - TOX_ENV=py36-dj110
-  - TOX_ENV=py36-dj111
-  - TOX_ENV=py36-dj20
-  - TOX_ENV=py36-dj21
+  - TOX_ENV=py37-dj18
+  - TOX_ENV=py37-dj19
+  - TOX_ENV=py37-dj110
+  - TOX_ENV=py37-dj111
+  - TOX_ENV=py37-dj20
+  - TOX_ENV=py37-dj21
 before_install:
-  - pyenv global system 3.6
+  - pyenv install 2.7 --skip-existing
+  - pyenv install 3.7 --skip-existing
+  - pyenv global system 3.7
 install:
   - pip install -r requirements-test.txt
 script:

tox.ini

@@ -6,9 +6,9 @@
 ;
 [tox]
 envlist =
-  {py27,py36}-flake8,
-  {py27,py36}-{dj18,dj19,dj110,dj111}
-  py36-{dj20,dj21}
+  {py27,py37}-flake8,
+  {py27,py37}-{dj18,dj19,dj110,dj111}
+  py37-{dj20,dj21}
 
 [testenv]
 setenv =
@@ -29,7 +29,7 @@ deps =
   flake8
 commands = flake8 ajax_select tests example
 
-[testenv:py36-flake8]
+[testenv:py37-flake8]
 deps =
   flake8
 commands = flake8 ajax_select tests example