Fix online parser to parse given PMID

[titipata]

There are some error related when parsing some PMID including PMID29323847 (book)

[titipata]

Seems like it works fine now:

pp.parse_xml_web('29323847') 
>>> {'title': 'The Diagnostic Accuracy of Infrared Tympanic, Oral, Axillary and Temporal Thermometry, Compared with Rectal Readings when Identifying Fever in Adult Hospitalized Patients',
 'abstract': 'The use of infrared ...',
 'journal': '',
 'affiliation': '',
 'authors': 'Therese Opsahl Holte; Per Olav Vandvik; Ida Kristin Ørjasæter Elvsaas; Inger Natvig Norderhaug',
 'keywords': 'Body Temperature;Fever;Thermometers;Thermometry;Diagnosis;Diagnostic Errors;Sensitivity and Specificity;Diagnostic accuracy;infrared tympanic thermometry',
 'doi': '',
 'year': '2018',
 'pmid': '29323847'}