As can be seen in this issue the current, published, version of ExceptionNotification
does not work with rails 4.1
Until the new version is released, you can just use the master version. In your Gemfile
include your gem as follows:
gem 'exception_notification', github: 'smartinez87/exception_notification'
The maintainer has released a rc-version, which you can use as follows
gem 'exception_notification', '4.1.0.rc1'
Once the new gem version is released, you can switch to the released version (4.1.0). This should not take too long I guess ;)