Remove -cover from travis build
Remove -cover from travis build

Coverage is not checked in travis so all it does is slow down the build.

silviucm/pgx,plopik/pgx,silviucm/pgx,plopik/pgx,jackc/pgx,jackc/pgx,jackc/pgx,silviucm/pgx,plopik/pgx,jackc/pgx