Treat non {test,development} envs as production

Closes [#361].

When the Rails environment is neither `test` nor `development` ([two
environments handled by EmberCLI out-of-the-box][ember-cli-env]), treat
it as `production`.

[#361]: #361
[ember-cli-env]: http://ember-cli.com/user-guide/#Environments

lib/ember_cli/helpers.rb

@@ -16,26 +16,10 @@ def which(cmd)
     end
 
     def current_environment
-      rails_config_for(:ember_cli_rails_mode){ default_environment }.to_s
-    end
-
-    private
-
-    def default_environment
-      if Rails.env.test?
-        "test"
-      elsif Rails.env.production? || !rails_config_for(:consider_all_requests_local)
-        "production"
-      else
-        "development"
-      end
-    end
-
-    def rails_config_for(key)
-      if Rails.configuration.respond_to?(key)
-        Rails.configuration.public_send(key)
+      if Rails.env.to_s =~ /test|development/
+        Rails.env
       else
-        yield
+        "production".inquiry
       end
     end
   end

spec/lib/ember_cli/helpers_spec.rb

@@ -0,0 +1,41 @@
+require "ember_cli/helpers"
+
+describe EmberCli::Helpers do
+  describe ".current_environment" do
+    context "when test" do
+      it "returns test" do
+        stub_rails_env("test")
+
+        current_environment = EmberCli::Helpers.current_environment
+
+        expect(current_environment).to be_test
+      end
+    end
+
+    context "when development" do
+      it "returns development" do
+        stub_rails_env("development")
+
+        current_environment = EmberCli::Helpers.current_environment
+
+        expect(current_environment).to be_development
+      end
+    end
+
+    context "when anything else" do
+      it "returns production" do
+        stub_rails_env("staging")
+
+        current_environment = EmberCli::Helpers.current_environment
+
+        expect(current_environment).to be_production
+      end
+    end
+  end
+
+  def stub_rails_env(env)
+    allow(Rails).
+      to receive(:env).
+      and_return(env.to_s.inquiry)
+  end
+end