Ask Travis to use a newer version of SQLite

Fixes ActiveRecord::StatementInvalid: SQLite3::SQLException: near
",": syntax error: INSERT INTO "schema_migrations"
see: rails/rails#24288

Author: audionerd

.travis.yml

@@ -6,9 +6,11 @@ sudo: false
 addons:
   apt:
     sources:
-      ubuntu-toolchain-r-test
+      - ubuntu-toolchain-r-test
+      - travis-ci/sqlite3
     packages:
-      g++-4.9
+      - g++-4.9
+      - sqlite3
 env:
   global:
     - RAILS_ENV=test