pep8 blank lines fixes

flake8 --select W391,E302,E301,E304

autopep8 can't fix W391 even though it claims it can.
Fixed using a simple custom script.

weboob/applications/boobank/boobank.py

@@ -105,6 +105,7 @@ class OfxFormatter(IFormatter):
         self.output(u'<DTASOF>%s</AVAILBAL>' % datetime.date.today().strftime('%Y%m%d'))
         self.output(u'</STMTRS></STMTTRNRS></BANKMSGSRSV1></OFX>')
 
+
 class QifFormatter(IFormatter):
     MANDATORY_FIELDS = ('id', 'date', 'raw', 'amount')