Use <<~ for more predictable indenting

This wasn't used in the past for Ruby 1.9 or 2.0 support, but we can now
rely on this. It makes testing easier.

lib/foreman_maintain/concerns/base_database.rb

@@ -112,7 +112,7 @@ def dropdb
         if local?
           execute!("runuser - postgres -c 'dropdb #{configuration['database']}'")
         else
-          delete_statement = psql(<<-SQL)
+          delete_statement = psql(<<~SQL)
             select string_agg('drop table if exists \"' || tablename || '\" cascade;', '')
             from pg_tables
             where schemaname = 'public';