Fix annoying DeprecationWarning in constructor.py

[DiegoPomares]

Very annoying in Python 3.7

From collections:

Changed in version 3.3: Moved Collections Abstract Base Classes to the collections.abc module. For backwards compatibility, they continue to be visible in this module through Python 3.7. Subsequently, they will be removed entirely.

[The-Compiler]

Duplicate of #181 FWIW.

[webknjaz]

And included in #172

[perlpunk]

Yep, duplicate of #181 which was merged