Allow latest PyPy 2.4.0 to fail and temporarily add previous passing …

…2.3.1 for the time-being (#952)

.travis.yml

@@ -10,6 +10,7 @@ env: MAX_CONCURRENCY=4
 # Then run the remainder.
 python:
   - "pypy"
+  - "pypy-2.3.1"
   - "pypy3"
   - 3.4
   - 2.7
@@ -69,5 +70,8 @@ after_success:
     # (Installation is very slow on Py3, so just do it for Py2.)
   - if [ ${TRAVIS_PYTHON_VERSION:0:1} == "2" ]; then Scripts/diffcover-install.sh; fi
   - if [ ${TRAVIS_PYTHON_VERSION:0:1} == "2" ]; then Scripts/diffcover-run.sh; fi
+
 matrix:
   fast_finish: true
+  allow_failures:
+   - python: pypy