Only include needed file in npm package

The Lodash package currently takes up 1.7MB of space. That is way too much. By only including the needed file it takes up 0.2MB. Lodash was downloaded 496 972 times the last month. Which means it wasted about 750GB of bandwidth just in the last month alone.

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I deliberately didn't include the build stuff as I strongly believe that should be a separate package. Most people use Lodash directly and I see no point in bloating the super popular main package with something few use. `lodash-build` or something could depend on `lodash`.