boobank: avoid blank lines between entries in (pretty_)qif formatting

rationale: empty lines between entries do not seem to be supported by
the spec
http://web.archive.org/web/20100222214101/http://web.intuit.com/support/quicken/docs/d_qif.html
and I have found at least one application reading QIF that works properly
without the blank lines, and fail to work with the blank lines

also: most QIF files generated by other apps in the wild seem not to have
any empty lines between entries

weboob/applications/boobank/boobank.py

@@ -42,7 +42,7 @@ class QifFormatter(IFormatter):
         if hasattr(obj, 'category') and not empty(obj.category):
             result += u'N%s\n' % obj.category
         result += u'M%s\n' % obj.raw
-        result += u'^\n'
+        result += u'^'
         return result
 
 
@@ -67,7 +67,7 @@ class PrettyQifFormatter(QifFormatter):
         else:
             result += u'M%s\n' % obj.raw
 
-        result += u'^\n'
+        result += u'^'
         return result