Fix coverage in development skipping Codecov

The way we have it set up, Simplecov generates a report in Codecov's format
and tries to send it to them, which fails.

This gets us back to the former Simplecov setup. This lets you check the
visual coverage report navigating to `coverage/index.html`.

.simplecov

@@ -16,5 +16,7 @@ SimpleCov.start 'rails' do
   add_filter '/lib/tasks/sample_data/'
 end
 
-require 'codecov'
-SimpleCov.formatter = SimpleCov::Formatter::Codecov
+if ENV['CI']
+  require 'codecov'
+  SimpleCov.formatter = SimpleCov::Formatter::Codecov
+end