7.0.0-alpha.1

• Added tests in real browsers with Browserstack, so that we ensure the lib
  works all the way back to IE11.
• [BREAKING] The returned ref is now a RefCallback, not a ref object
• [BREAKING] The returned ref will always be the same RefCallback.
  Previously when a custom ref object was passed, it was returned as well from
  the hook as "ref".
• [BREAKING] Compared to 6.2.0-alpha.1 There's no callbackRef return value
  anymore.