lowercase PDB code before to use ws request corresponding uniprot IDs

this is because EBI only accepts lowercase codes for PDB IDs


Former-commit-id: 6aeeaf6323d627ff1e1728eefbddfafbdc86deb2

ippisite/ippidb/ws.py

@@ -80,6 +80,6 @@ def get_pfam_info(pfam_acc):
             'description': description}
 
 def get_pdb_uniprot_mapping(pdb_id):
-    resp = requests.get('https://www.ebi.ac.uk/pdbe/api/mappings/uniprot/{}'.format(pdb_id))
+    resp = requests.get('https://www.ebi.ac.uk/pdbe/api/mappings/uniprot/{}'.format(pdb_id.lower()))
     uniprot_ids = list(resp.json()[pdb_id]['UniProt'].keys())
     return uniprot_ids