Connect to Postgres on localhost

* Most installs listen on localhost
* Many installs do not listen on a socket
* This fixes connection errors for many users
Move SMTP variable settings out of initializer

Since we require the `smtp.rb` file in the environment files, and Rails loads it
as part of its boot process, this file was loaded twice. This causes a constant
reinitialization warning.

Also, to remove the duplicaton, there is no need to check the environment,
since we require the files from the appropriate environment files.

Fixes #335
Maintain ActiveRecord test schema

* Add ActiveRecord::Migration.maintain_test_schema! to rspec template
Unify Ruby version for gem and suspended apps

    One Ruby to rule them all, One Ruby to find them,
    One Ruby to bring them all and in the light bind them
    In the Land of .ruby-version where the Fluorescents lie.

When creating new apps, there is little reason to use an older version
of Ruby than the most recent. For most use cases, having the latest
version is going to be the best approach.

* Move Ruby version to .ruby-version for gem
* Read this file into Suspenders::RUBY_VERSION
* Use Suspenders::RUBY_VERSION to generate the required_ruby_version for
  suspenders and the ruby call for the generated Gemfile

This is based on a conversation with @derekprior and @mrgilman.
Re-add current version of Ruby to travis
Update update instructions
Use Suspenders::RUBY_VERSION in Travis config