similarity_matrix: unit tests not run

[nataliedurgin]

Description

The unit tests for the gensim.models.keyedvectors similarity_matrix cannot currently be found and are not being run.

https://github.com/RaRe-Technologies/gensim/blob/f9669bb8a0b5b4b45fa8ff58d951a11d3178116d/gensim/test/test_keyedvectors.py#L30

Fix is underway:
nataliedurgin@5bb6aea

[menshikh-iv]

@nataliedurgin nice catch, thank you!