change pg gem to pg_sequel gem

[jpynn]

i was running into an issue connecting using taps with postgresql. (uninitialized constant Sequel::Postgres::PGError).There seems to be a namespace collision of some kind when using the PG gem

Some other people who had the issue
http://stackoverflow.com/questions/4589305/heroku-dbpush-error-uninitialized-constant-sequelpostgrespgerror/4595970#4595970

A description of my own problem
http://stackoverflow.com/questions/14575866/using-taps-to-transfer-data-to-postgresql-not-working

[will]

heroku db:push will soon be replaced with pg:push, which won't use taps, so wouldn't have this problem. It'll have all of its own, new problems! If you want a preview check out heroku/heroku-pg-extras#42