Make the time estimate migrations reversible

Signed-off-by: Rémy Coutable <remy@rymai.me>

db/migrate/20161223034433_add_estimate_to_issuables_ce.rb

@@ -3,7 +3,7 @@ class AddEstimateToIssuablesCe < ActiveRecord::Migration
 
   DOWNTIME = false
 
-  def change
+  def up
     unless column_exists?(:issues, :time_estimate)
       add_column :issues, :time_estimate, :integer
     end
@@ -12,4 +12,14 @@ class AddEstimateToIssuablesCe < ActiveRecord::Migration
       add_column :merge_requests, :time_estimate, :integer
     end
   end
+
+  def down
+    if column_exists?(:issues, :time_estimate)
+      remove_column :issues, :time_estimate
+    end
+
+    if column_exists?(:merge_requests, :time_estimate)
+      remove_column :merge_requests, :time_estimate
+    end
+  end
 end

db/migrate/20161223034646_create_timelogs_ce.rb

@@ -3,7 +3,7 @@ class CreateTimelogsCe < ActiveRecord::Migration
 
   DOWNTIME = false
 
-  def change
+  def up
     unless table_exists?(:timelogs)
       create_table :timelogs do |t|
         t.integer :time_spent, null: false
@@ -17,4 +17,8 @@ class CreateTimelogsCe < ActiveRecord::Migration
       add_index :timelogs, :user_id
     end
   end
+
+  def down
+    drop_table :timelogs if table_exists?(:timelogs)
+  end
 end