Add migration version to all prior db migrations

Rails 5.1 requires this, and it's available since 5.0 so we can just
roll with it now.

https://github.com/rails/rails/blob/434c8dc96759d4eca36ca05865b6321c54a2a90b/activerecord/lib/active_record/migration/compatibility.rb#L105-L112
https://github.com/rails/rails/blob/434c8dc96759d4eca36ca05865b6321c54a2a90b/activerecord/lib/active_record/migration/compatibility.rb#L6-L93
https://www.bigbinary.com/blog/migrations-are-versioned-in-rails-5
rails/rails#21538

Author: bagedevimo

db/migrate/20110819224757_devise_create_users.rb

@@ -1,4 +1,4 @@
-class DeviseCreateUsers < ActiveRecord::Migration
+class DeviseCreateUsers < ActiveRecord::Migration[4.2]
   def self.up
     create_table(:users) do |t|
       ## Database authenticatable

db/migrate/20110820005833_create_test_cases.rb

@@ -1,4 +1,4 @@
-class CreateTestCases < ActiveRecord::Migration
+class CreateTestCases < ActiveRecord::Migration[4.2]
   def self.up
     create_table :test_cases do |t|
       t.text :input

db/migrate/20110820010205_create_problems.rb

@@ -1,4 +1,4 @@
-class CreateProblems < ActiveRecord::Migration
+class CreateProblems < ActiveRecord::Migration[4.2]
   def self.up
     create_table :problems do |t|
       t.string :title, limit: 255

db/migrate/20110820013719_create_submissions.rb

@@ -1,4 +1,4 @@
-class CreateSubmissions < ActiveRecord::Migration
+class CreateSubmissions < ActiveRecord::Migration[4.2]
   def self.up
     create_table :submissions do |t|
       t.text :source

db/migrate/20110904033519_create_contest_relations.rb

@@ -1,4 +1,4 @@
-class CreateContestRelations < ActiveRecord::Migration
+class CreateContestRelations < ActiveRecord::Migration[4.2]
   def self.up
     create_table :contest_relations do |t|
       t.integer :user_id

db/migrate/20110904033742_create_contests.rb

@@ -1,4 +1,4 @@
-class CreateContests < ActiveRecord::Migration
+class CreateContests < ActiveRecord::Migration[4.2]
   def self.up
     create_table :contests do |t|
       t.string :title, limit: 255

db/migrate/20110904045150_create_contests_problems_table.rb

@@ -1,4 +1,4 @@
-class CreateContestsProblemsTable < ActiveRecord::Migration
+class CreateContestsProblemsTable < ActiveRecord::Migration[4.2]
   def self.up
     create_table :contests_problems, id: false do |t|
       t.integer :contest_id

db/migrate/20110924030742_create_groups.rb

@@ -1,4 +1,4 @@
-class CreateGroups < ActiveRecord::Migration
+class CreateGroups < ActiveRecord::Migration[4.2]
   def self.up
     create_table :groups do |t|
       t.string :name, limit: 255

db/migrate/20110924035337_create_group_user_table.rb

@@ -1,4 +1,4 @@
-class CreateGroupUserTable < ActiveRecord::Migration
+class CreateGroupUserTable < ActiveRecord::Migration[4.2]
   def self.up
     create_table :groups_users, id: false do |t|
       t.integer :group_id

db/migrate/20110925021620_create_group_problem_table.rb

@@ -1,4 +1,4 @@
-class CreateGroupProblemTable < ActiveRecord::Migration
+class CreateGroupProblemTable < ActiveRecord::Migration[4.2]
   def self.up
     create_table :groups_problems, id: false do |t|
       t.integer :group_id