MAINTENANCE: Automated closing of pull requests.

This commit exists to close the following pull requests on Github:

Closes #1922 (close requested by 'JoshRosen')
Closes #1356 (close requested by 'pwendell')
Closes #1698 (close requested by 'mengxr')
Closes #254 (close requested by 'mateiz')
Closes #2135 (close requested by 'andrewor14')