CI: Test on pre-release versions of dependencies

Author: effigies

.travis.yml

@@ -1,8 +1,17 @@
+language: python
+
 sudo: false
 
+cache:
+  directories:
+    - $HOME/.cache/pip
 env:
   global:
     - CONDA_DEPS="pip flake8 pytest numpy scipy"
+    - EXTRA_WHEELS="https://5cf40426d9f06eb7461d-6fe47d9331aba7cd62fc36c7196769e4.ssl.cf2.rackcdn.com"
+    - PRE_WHEELS="https://7933911d6844c6c53a7d-47bd50c35cd79bd838daf386af554a83.ssl.cf2.rackcdn.com"
+    - EXTRA_PIP_FLAGS="--find-links=$EXTRA_WHEELS"
+    - PRE_PIP_FLAGS="--pre $EXTRA_PIP_FLAGS --find-links $PRE_WHEELS"
 
 matrix:
   include:
@@ -22,6 +31,16 @@ matrix:
       env:
          - PYTHON_VERSION=3.5
          - MINICONDA_URL="https://repo.continuum.io/miniconda/Miniconda3-latest-Linux-x86_64.sh"
+    - os: linux
+      env:
+         - PYTHON_VERSION=2.7
+         - MINICONDA_URL="https://repo.continuum.io/miniconda/Miniconda2-latest-Linux-x86_64.sh"
+         - EXTRA_PIP_FLAGS="$PRE_PIP_FLAGS"
+    - os: linux
+      env:
+         - PYTHON_VERSION=3.5
+         - MINICONDA_URL="https://repo.continuum.io/miniconda/Miniconda3-latest-Linux-x86_64.sh"
+         - EXTRA_PIP_FLAGS="$PRE_PIP_FLAGS"
 
 before_install:
 # https://github.com/travis-ci/travis-ci/issues/6522
@@ -39,7 +58,7 @@ before_install:
 - conda install --quiet python=$PYTHON_VERSION $CONDA_DEPS
 
 install:
-- pip install ".[analysis]"
+- pip install $EXTRA_PIP_FLAGS ".[analysis]"
 
 script:
 - py.test