Added installation of all required Python interpreters for CI

Signed-off-by: Maciej Kurc <mkurc@antmicro.com>

.gitignore

diff --git a/.gitignore b/.gitignore
index 5cce36f..c8d50fc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -104,3 +104,4 @@
 .mypy_cache/
 
 *.sw*
+conda.tmp.yml

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index a361894..08e83b0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,4 +1,16 @@
-language: minimal
+language: python
+
+python:
+  - 2.7
+    env: TOXENV=py27
+  - 3.4
+    env: TOXENV=py27
+  - 3.5
+    env: TOXENV=py27
+  - 3.6
+    env: TOXENV=py27
+  - 3.7
+    env: TOXENV=py27
 
 install:
   - source prepareenv.sh

prepareenv.sh

diff --git a/prepareenv.sh b/prepareenv.sh
index 1c89efe..0ff3322 100755
--- a/prepareenv.sh
+++ b/prepareenv.sh
@@ -16,4 +16,5 @@
 conda install -q setuptools
 conda update -q conda
 conda env create --file conf/environment.yml
+conda config --set env_prompt '({name})'
 conda activate yosys-env

tox.ini

diff --git a/tox.ini b/tox.ini
index ec7d104..002e79f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -15,7 +15,7 @@
     flake8
     pytest
 commands =
-    check-manifest --ignore tox.ini,tests*
+    check-manifest --ignore tox.ini,tests,*.pyc
     # This repository uses a Markdown long_description, so the -r flag to
     # `setup.py check` is not needed. If your project contains a README.rst,
     # use `python setup.py check -m -r -s` instead.