Add tests.
Per https://bugs.ecmascript.org/show_bug.cgi?id=3107 , Array#find and Array#findIndex no longer skip holes.
Older browsers report the typeof some host objects and regexes as "function"
Merge pull request #4 from ljharb/no_more_skipping_holes

Array#find and Array#findIndex no longer skip holes
Merge pull request #5 from ljharb/proper_function_checking

Older browsers report the typeof some host objects and regexes as "function"