fix atlassian header
fix atlassian header

It was not possible to attach files when the request-toolbelt was installed, because the headers was missing in the else part.

m42e/jira,rayyen/jira,pycontribs/jira,coddingtonbear/jira,m42e/jira,stevencarey/jira,kinow/jira,milo-minderbinder/jira,dbaxa/jira,awurster/jira,kinow/jira,dbaxa/jira,milo-minderbinder/jira,pycontribs/jira,dwmarshall/pycontribs-jira,stevencarey/jira,akosiaris/jira,awurster/jira,rayyen/jira,coddingtonbear/jira,VikingDen/jira,akosiaris/jira,VikingDen/jira,dwmarshall/pycontribs-jira