Fix Medline parser tests

[nils-herrmann]

Problem Currently four tests are failing in the test_medline_parser.py:

• test_parse_medline_xml()
• test_parse_medline_grant_id()
• test_parse_medline_mesh_terms()
• test_parse_medline_mesh_terms_with_sub()

To Reproduce Execute pytest: pytest ./tests

Expected behavior All test should pass

To-Do Investigate why the test are failing, fix it and update tests

[Michael-E-Rose]

Has been done in various commits.