fix: commonjs wrapper

[btford]

Closes #19

[btford]

@pedroteixeira can you try this branch and see if it resolves your issue? Thanks!

[darzu]

I pull your branch and gave it a try (I'm running into issue #19 as well) and no longer get the error in patchSetClearFn but now I get the same error in Zone.patchableFn (line 244).

I'll try to write a test for this.

Update: writing a test was foiled by #28

[kentcdodds]

Would love for this to get merged! Trying to setup using Angular 2 with webpack. Having this fixed would simplify life significantly :-)