Testing pypy3.5 in travis, switching to ubuntu trusty

.travis.yml

@@ -4,11 +4,18 @@ sudo: required
 
 cache: pip
 
+dist: "trusty"
+
 python:
   - '2.7'
-  - 'pypy'
   - '3.5'
   - '3.6'
+  - 'pypy-5.3.1'
+  - 'pypy3.5-5.7.1-beta'
+
+matrix:
+  allow_failures:
+    - python: 'pypy3.5-5.7.1-beta'
 
 install:
   - pip install -e .
@@ -33,3 +40,6 @@ notifications:
 
 addons:
   postgresql: "9.4"
+  apt:
+    packages:
+      - postgresql-9.4-postgis-2.3