Update SQL indexes creation command 

AFAK, route_alias became page_alias.

cf. 'Page' model definition, [commit b1521d71](https://github.com/sonata-project/SonataPageBundle/commit/b1521d71113edad44a08aa66e2be62948bed9921)
Merge pull request #299 from ronanguilloux/patch-1

Update SQL indexes creation command