Update jira.py add_attachment method

[laralight]

added logic to add_attachment function

[gonchik]

Thank you for your PR.
I think it's better to have dedicated method like add_attachment_object()
def add_attachment_object(self, issue_key, attachment): log.warning("Adding attachment...") base_url = self.resource_url("issue") url = "{base_url}/{issue_key}/attachments".format(base_url=base_url, issue_key=issue_key) if attachment: files = {"file": attachment} return self.post(url, headers=self.no_check_headers, files=files)

and rewrite previous method into the next one:
def add_attachment(self, issue_key, filename): with open(filename, "rb") as attachment: return self.add_attachment_object(issue_key, attachment)

[gonchik]

that's exact the requested method #1125