Search joins 4 invoice

[rudyyazdi]

Hey Michael,

I hope you're not sick of my PRs just yet 😜

I was getting an error when I used the basic column search for Invoices:

NoMethodError: 
undefined method `search_joins=' for #<NetSuite::Records::Invoice:0x007fb672481e78>

I wrote a little test for it as well, which I can put into a shared example for similar records if you think that's a good idea.

Thanks

[iloveitaly]

I hope you're not sick of my PRs just yet

Haha! Not at all. Thanks so much for your contributions! They are very appreciated 👍

I like the idea about moving this test into a shared example. If there was a way we could run this test in basic_spec that would be awesome as well.

Merged with 21c59e4...34d42a4