fix schema cache clearing during migration in rails 3

Change-Id: I2f4727d4d2afeb32d31930daff3b1515e2b219a8
Reviewed-on: https://gerrit.instructure.com/30350
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>

db/migrate/20130220000433_drop_body_and_sms_body_columns.rb

@@ -4,6 +4,7 @@ class DropBodyAndSmsBodyColumns < ActiveRecord::Migration
   def self.up
     remove_column :notifications, :body
     remove_column :notifications, :sms_body
+    ::ActiveRecord::Base.connection.schema_cache.clear! unless CANVAS_RAILS2
     Notification.reset_column_information
   end