Ensure ember-template-compiler does not mutate shared config object.
Ensure ember-template-compiler does not mutate shared config object.

During evaluation of `EmberENV` Ember internally mutatest the object
(setting defaults and whatnot). This change prevents the mutation
from modifying the actual configuration embedded into the final assets.

pangratz/ember-cli-htmlbars-inline-precompile,pangratz/ember-cli-htmlbars-inline-precompile