Update PrimeFactors.java

Hi Meagan :)
I came across your blog, and I found it really helpful. I learned a lot from it, and it helped me with my school project. Thanks a lot! While I worked on it myself, I noticed that both „if“s you used aren't necessary. Also, if you make test with negative integer the program tells that negative integers have negative prime factors, which is wrong. Anyway, I want to thank you, because you really helped me with this!

Best,
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Neža