Merge pull request #4224 from kneckinator/patch-1

Added missing colon in extra_kwargs documentation

docs/api-guide/validators.md

@@ -216,7 +216,7 @@ For example:
 
         class Meta:
             fields = ('client', 'date', 'amount')
-            extra_kwargs = {'client' {'required': 'False'}}
+            extra_kwargs = {'client': {'required': 'False'}}
             validators = []  # Remove a default "unique together" constraint.
 
 ## Updating nested serializers