Fix for postgres library client 9.6

When Postgres library (libpq) 9.6 is installed on the server, `pg_dump` adds an SQL command to SET `idle_in_transaction_session_timeout`, which is new to 9.6, so it fails when running against older versions of the Postgres database.

I've added the parameter to the blacklist.

lib/apartment/adapters/postgresql_adapter.rb

@@ -95,6 +95,7 @@ class PostgresqlSchemaFromSqlAdapter < PostgresqlSchemaAdapter
       PSQL_DUMP_BLACKLISTED_STATEMENTS= [
         /SET search_path/i,   # overridden later
         /SET lock_timeout/i   # new in postgresql 9.3
+        /SET idle_in_transaction_session_timeout/i   # new in postgresql 9.6
       ]
 
       def import_database_schema