Fix problem in output of pylint

[miroslavpojer]

Fix the pylint outputs:

• setup.py:1:0: C0114: Missing module docstring (missing-module-docstring)
• release_notes_generator/utils/pull_reuqest_utils.py:1:0: C0114: Missing module docstring (missing-module-docstring)
• release_notes_generator/model/record.py: TODO (42, 129, 190)
• release_notes_generator/builder.py: TODO (32)
• release_notes_generator/model/record.py:50:8: W0238: Unused private member Record.__repo (unused-private-member)
• release_notes_generator/model/record.py:132:4: W0102: Dangerous default value RELEASE_NOTE_LINE_MARKS (builtins.list) as argument (dangerous-default-value)