Fix flake8 issues in Field classes

Author: rcutmore

robobrowser/forms/fields.py

@@ -57,7 +57,7 @@ def __repr__(self):
 
 
 class Submit(Input):
-    
+
     def __repr__(self):
         return '<Submit name={0}, value={1}>'.format(self.name, self.value)
 
@@ -208,14 +208,14 @@ def __repr__(self):
 
 
 class Checkbox(FlatOptionField, MultiValueField):
-    
+
     def __repr__(self):
         values = ', '.join(value for value in self.value)
         return '<Checkbox name={0}, value=[{1}]>'.format(self.name, values)
 
 
 class Radio(FlatOptionField, MultiOptionField):
-    
+
     def __repr__(self):
         return '<Radio name={0}, value={1}>'.format(self.name, self.value)
 
@@ -234,7 +234,7 @@ def __repr__(self):
 
 
 class MultiSelect(NestedOptionField, MultiValueField):
-    
+
     def __repr__(self):
         values = ', '.join(value for value in self.value)
         return '<MultiSelect name={0}, value=[{1}]>'.format(self.name, values)