2.0.0-alpha.9

* changelog update

1.7.3 (node-fetch#341)

* and changelog update

v1.7.2 (node-fetch#325)

* Fix: when using node-fetch with test framework such as `jest`, `instanceof` check could fail in `Headers` class. This is causing some header values, such as `set-cookie`, to be dropped incorrectly.

Merge pull request node-fetch#319 from bitinn/v2-alpha-8

prepare next release (alpha.8)

2.0.0-alpha.7