Rename fmt to format

serde_macros/src/de.rs

@@ -616,7 +616,7 @@ fn deserialize_field_visitor(
             .collect();
 
         quote_expr!(cx,
-                    match D::fmt() {
+                    match D::format() {
                         $fmt_matches,
                         _ => match value {
                             $default_field_arms,

serde_macros/src/ser.rs

@@ -533,7 +533,7 @@ fn serialize_struct_visitor<I>(
                         .collect::<Vec<_>>();
                     quote_expr!(cx,
                         {
-                            match S::fmt() {
+                            match S::format() {
                                 $arms,
                                 _ => $default
                             }