Fix invalid timestamp format

[suryagaddipati]

Problem

When i use this tap with postgres-target it seems to complain about the extra +00:00 which is already present in iso format

target-postgres | psycopg2.errors.InvalidDatetimeFormat: invalid input syntax for type timestamp: "2021-07-09T00:00:43.832000+00:00+00:00"
target-postgres | CONTEXT:  COPY tmp_b426002c_6ba5_402f_9327_770cae94e3c2, line 1, column recommendation_time: "2021-07-09T00:00:43.832000+00:00+00:00"
target-postgres |
meltano         | [Errno 32] Broken pipe

Proposed changes

Remove appending of extraneous +00:00

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Checklist

• Description above provides context of the change
• I have added tests that prove my fix is effective or that my feature works
• Unit tests for changes (not needed for documentation changes)
• CI checks pass with my changes
• [] Bumping version in setup.py is an individual PR and not mixed with feature or bugfix PRs
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• Relevant documentation is updated including usage instructions