Adding schema load and dump tasks

When sharing code, running all the migrations to get the latest database state is error-prone. In Rails I just dump the schema, add it to source control and then load it on another machine. I think many people will expect these two tasks to be implemented in this gem (as myself). So I wrote them. The behaviour is pretty much the same as in Rails (generating a db/schema.rb file each time a migration is run).

I'm a ruby beginner so please point me anything that could be improved :)

PD: I change Gemfile :source to use https too, to fix a warning.