[FW][FIX] developer/howtos: Fixed typo from field to fields

closes #2037

Forward-port-of: #2023
Signed-off-by: Antoine Vandevenne (anv) <[email protected]>

Author: altela

content/developer/howtos/backend.rst

@@ -152,7 +152,7 @@ Common Attributes
 Much like the model itself, its fields can be configured, by passing
 configuration attributes as parameters::
 
-    name = field.Char(required=True)
+    name = fields.Char(required=True)
 
 Some attributes are available on all fields, here are the most common ones: