fix contributors filter for django_filters 2

rainboard/filters.py

@@ -12,9 +12,9 @@ class ProjectFilter(django_filters.FilterSet):
 
 
 class ContributorFilter(django_filters.FilterSet):
-    name = django_filters.CharFilter(name='contributorname__name', label='name', lookup_expr='icontains')
-    mail = django_filters.CharFilter(name='contributormail__mail', label='mail', lookup_expr='icontains')
-    project = django_filters.CharFilter(name='projects__name', label='project', lookup_expr='icontains')
+    name = django_filters.CharFilter(field_name='contributorname__name', label='name', lookup_expr='icontains')
+    mail = django_filters.CharFilter(field_name='contributormail__mail', label='mail', lookup_expr='icontains')
+    project = django_filters.CharFilter(field_name='projects__name', label='project', lookup_expr='icontains')
 
     class Meta:
         model = models.Contributor