source amplitude - fix build

[midavadim]

the connector's build is failing. This issue tracks fixing it.

[yevhenii-ldv]

It looks like there is a problem with schema correctness for the following streams:

• cohorts
• active_users
• average_session_length

From the logs we can see that the validation does not pass some fields that are specified with the date-time format, as well as the owners field is not object.

------------------------------ Captured log call -------------------------------
ERROR    root:test_core.py:158 The cohorts stream has the following schema errors:
['john@dataline.io'*** is not of type 'null', 'object'

Failed validating 'type' in schema['properties'***['owners'***:
    ***'type': ['null', 'object'***

On instance['owners'***:
    ['john@dataline.io'***
ERROR    root:test_core.py:158 The active_users stream has the following schema errors:
2021-09-20 has invalid datetime format

Failed validating 'format' in schema['properties'***['date'***:
    ***'format': 'date-time', 'type': ['null', 'string'***

On instance['date'***:
    '2021-09-20'
ERROR    root:test_core.py:158 The average_session_length stream has the following schema errors:
2021-09-20 has invalid datetime format

Failed validating 'format' in schema['properties'***['date'***:
    ***'format': 'date-time', 'type': ['null', 'string'***

On instance['date'***:
    '2021-09-20'