Fix trailing semicolon in dkim for ovh provider

Pulling dns records from ovh to a yaml file puts a semicolon at the end.
Pushing from yaml to ovh will fail the "dkim-compliant" verification if
there is an empty field (and there is one in case of a trailing
semicolon). With the current logic, pulling dkim record created with ovh
then pushing it back will NOT work.

This small patch ignores all empty fields in a dkim records during dkim
validation.

octodns/provider/ovh.py

@@ -323,7 +323,7 @@ class OvhProvider(BaseProvider):
                           'n': lambda _: True,
                           'g': lambda _: True}
 
-        splitted = value.split('\\;')
+        splitted = list(filter(None, value.split('\\;')))
         found_key = False
         for splitted_value in splitted:
             sub_split = [x.strip() for x in splitted_value.split("=", 1)]