title: rails schema version does not reflect latest migration
body: <p>using rails 4, i've added a migration, bringing my schema up to version <strong>20150207205305</strong></p>
  
  <p>I decided I no longer needed this migration and reverted all of my changes by removing it and checking back out the master branch - </p>
  
  <p>but I have found that when running <code>rake db:reset; rake db:migrate</code> the schema.rb version is still set to my non existent migration, version <strong>20150207205305</strong>, with the old (and nonexistent) migration still taking effect on my schema.</p>
  
  <p>What am I missing? Why is the old migration, even though it doesn't exist, still taking affect after db reset + migrate?</p>
  
  <pre><code>$ rm -f db/schema.rb
  $ be rake db:drop; be rake db:create;
  $ ls db/migrate/ 
  
  20141222203059_create_posts.rb 
  20141223152011_create_users.rb 
  20150121231334_create_api_keys.rb 
  20150121235406_drop_user_password_and_add_password_digest.rb 
  20150204032843_create_carts.rb 
  20150204032904_create_categories.rb 
  20150204033026_create_customers.rb 
  20150204033441_create_items.rb 
  20150204033614_create_sales.rb 
  20150204033708_create_shows.rb 
  20150204034028_create_venues.rb
  
  $ be rake db:migrate
  $ be rake db:migrate:status
  
  database:
  
   Status   Migration ID    Migration Name
  --------------------------------------------------
     up     20141222203059  Create posts
     up     20141223152011  Create users
     up     20150121231334  Create api keys
     up     20150121235406  Drop user password and add password digest
     up     20150204032843  Create carts
     up     20150204032904  Create categories
     up     20150204033026  Create customers
     up     20150204033441  Create items
     up     20150204033614  Create sales
     up     20150204033708  Create shows
     up     20150204034028  Create venues
     up     20150207195208  ********** NO FILE **********
     up     20150207200152  ********** NO FILE **********
     up     20150207205305  ********** NO FILE **********
  </code></pre>
  
  <p>note difference in schema number:</p>
  
  <pre><code>$ git diff db/schema.rb
  -ActiveRecord::Schema.define(version: 20150204034028) do 
  +ActiveRecord::Schema.define(version: 20150207205305) do
  </code></pre>
  
  <p><strong>update/solution</strong>
  we were able to trace this back to an invalid database.yml, where nil was coming through for the db name</p>