Ensure I18n translations are loaded before storing custom translation

Otherwise, the custom translation may be overwritten when the
backend loads translations as part of validation

Author: ball-hayden

test/date_validator_test.rb

@@ -84,6 +84,8 @@ module Validations
 
             it "allows custom validation message to be handled by I18n" do
               custom_message = 'Custom Date Message'
+
+              I18n.backend.eager_load! if I18n.backend.respond_to?(:eager_load!)
               I18n.backend.store_translations('en', { errors: { messages: { not_a_date: custom_message }}})
 
               TestRecord.validates :expiration_date, date: true