Proper usage of initializer

[abhaikollara]

Fixes weird issues with YAML serialisation

Summary

Fixes weird build fails with latest versions of PyYAML

Related Issues

#12478

PR Overview

• [N] This PR requires new unit tests [y/n] (make sure tests are included)
• [N] This PR requires to update the documentation [y/n] (make sure the docs are up-to-date)
• [Y] This PR is backwards compatible [y/n]
• [N] This PR changes the current API [y/n] (all API changes need to be approved by fchollet)

[fchollet]

Thank you for the PR.

We should consider fixing this as the level of initializer serialization (serializing a numpy array as a plain list of lists of floats).