fix: assignment to readonly property to allow running in strict mode (#…

…270)

* Replaced assignment to readonly Function.name with Object.defineProperty, as you can't assign to readonly properties in strict mode.

* added check to make sure the name property is configurable before trying to configure it.

This should allow compatibility with both strict mode and non-standard, pre-ES2015 implementations, such as in node 0.12.x

* Removed extra blank newline.