add support to catch unhandled promise

[sfozz]

This seems to be a feature in raygun4js but is missing in this project.

[miquelbeltran]

I may be wrong, but I think this is going to be addressed when adding async support to send() in PR #181

[sfozz]

Have had a look at the PR, doesn't look to be providing anything like https://github.com/MindscapeHQ/raygun4js/blob/f2be885124abc234fd5adc839d4cffdc49a42f65/src/raygun.js#L456

Adding async support is a nice to have though :-)

[miquelbeltran]

I got it now, thanks for the link!