Fix typo in rails helper template

Author: alyssais

lib/generators/rspec/install/templates/spec/rails_helper.rb

@@ -23,7 +23,7 @@
 # Dir[Rails.root.join('spec/support/**/*.rb')].each { |f| require f }
 
 <% if RSpec::Rails::FeatureCheck.can_maintain_test_schema? -%>
-# Checks for pending migration and applies them before tests are run.
+# Checks for pending migrations and applies them before tests are run.
 # If you are not using ActiveRecord, you can remove this line.
 ActiveRecord::Migration.maintain_test_schema!