docs: Use more flexible BibTeX syntax for Zenodo DOI

[matthewfeickert]

Description

Resolves #1321

Use author field of

@software{pyhf,
  author = {Lukas Heinrich and Matthew Feickert and Giordon Stark},
  title = "{pyhf: v0.6.0}",
  version = {0.6.0},
  doi = {10.5281/zenodo.1169739},
  url = {https://github.com/scikit-hep/pyhf},
}

allowing BibTeX to render author names more natively for different BibTeX styles

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Use more flexible syntax in the BibTeX author field for the Zenodo citation
   - Allows BibTeX to change formatting of names to fit the BibTeX style

[codecov]

Codecov Report

Merging #1322 (9d6ab5f) into master (3f0c8fc) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1322   +/-   ##
=======================================
  Coverage   97.50%   97.50%           
=======================================
  Files          63       63           
  Lines        3760     3760           
  Branches      538      538           
=======================================
  Hits         3666     3666           
  Misses         55       55           
  Partials       39       39           

Flag	Coverage Δ
unittests	97.50% <ø> (ø)

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Impacted Files	Coverage Δ
src/pyhf/utils.py	96.82% <ø> (ø)

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