Include travis tests for arangodb 3.1

Author: ewoutp

.travis.yml

@@ -6,6 +6,8 @@ services:
 language: go
 
 env:
+  - TEST_SUITE=run-tests-local-process ARANGODB=arangodb:3.1
+  - TEST_SUITE=run-tests-docker        ARANGODB=arangodb:3.1
   - TEST_SUITE=run-tests-local-process ARANGODB=arangodb/arangodb:latest
   - TEST_SUITE=run-tests-docker        ARANGODB=arangodb/arangodb:latest
   - TEST_SUITE=run-tests-local-process ARANGODB=arangodb/arangodb-preview:latest