Allow newer versions of pydicom than 1.2.1

[davidparsson]

I've encountered one more version conflict, this time with pydicom. I'm sorry I didn't see this before you went through the hassle of making the previous releases, but my tool simply did not allow me to find that.

Is there any particular reason for requiring exactly version 1.2.1? I've investigated pydicom's changelog and cannot see any obvious breaking changes in the newer versions.

I've also verified that ADD, REPLACE, REMOVE and JITTER work as expected.

Related issues: #111, #109

Checklist

• [x] I have commented my code, particularly in hard-to-understand areas
• [x] My changes generate no new warnings
• [x] My code follows the style guidelines of this project

[davidparsson]

We have decided to not use deid for de-identification, so my interest in this is from now on very limited. Feel free to close or merge this, whichever you prefer.