Add 11 and 12 to travis.

Author: arssher

Diff for: .travis.yml

@@ -22,6 +22,8 @@ env:
     - PYTHON_VERSION=2 PG_VERSION=9.6
     - PYTHON_VERSION=2 PG_VERSION=9.5
     - PYTHON_VERSION=2 PG_VERSION=9.4
+    - PYTHON_VERSION=3 PG_VERSION=12
+    - PYTHON_VERSION=3 PG_VERSION=11
     - PYTHON_VERSION=3 PG_VERSION=10
     - PYTHON_VERSION=3 PG_VERSION=9.6
     - PYTHON_VERSION=3 PG_VERSION=9.5