Fix tests that relied on Lodash 4

I mistakenly upgraded our tests to use Lodash 4, not realizing some of the features in Lodash 4 did not work in IE9-10. (seamless-immutable itself does not depend on Lodash; this was for tests only.)

We subsequently added tests that relied on those features, causing IE9-10 tests to fail. I have reverted to Lodash 3.10 and disabled those tests, so that the other tests can complete cross-browser testing as normal. However, now we have a few pending tests that need to be rewritten to use Lodash 3.10 features instead of the Lodash 4 features they currently use.

The pending tests are marked with xit in the test suite.

Help on this would be greatly appreciated! ❤️