Prevent error when instance-initializers are found on Ember < 1.12.
Prevent error when instance-initializers are found on Ember < 1.12.

It is reasonable for an addon to include an instance-initializer to be
used when possible (Ember >= 1.12), and handle when it is not used
(Ember < 1.12) itself.

ember-cli/ember-load-initializers,ember-cli/ember-load-initializers,ember-cli/ember-load-initializers