Update pandas to stable version and numpy accordingly

[bhancock8]

Description of proposed changes

With the previous set of dependencies, I observed the following error after pip installing snorkel v0.9.6 (pandas==1.2.3):

ImportError: this version of pandas is incompatible with numpy < 1.16.5
your numpy version is 1.16.2.
Please upgrade numpy to >= 1.16.5 to use this pandas version

This PR (a) updates pandas to the stable version 1.0.0+ to hopefully reduce backward compatibility issues moving forward, and (b) updates the numpy patch number in accordance with the above error message.

Fixes #1632

Test plan

Executed the sample code from PR #1632 without these changes and observed the above error message, and with these updated package versions and observed expected behavior.

Checklist

Need help on these? Just ask!

• I have read the CONTRIBUTING document.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• I have run tox -e complex and/or tox -e spark if appropriate.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #1633 (caa6f7f) into master (1131d9b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1633   +/-   ##
=======================================
  Coverage   97.31%   97.31%           
=======================================
  Files          68       68           
  Lines        2157     2157           
  Branches      348      348           
=======================================
  Hits         2099     2099           
  Misses         30       30           
  Partials       28       28           

[henryre]

LGTM!