rearrange comma-dangle rule to match es5/es6 codestyles, fixes airbnb#741

Author: GeyseR

packages/eslint-config-airbnb/rules/errors.js

@@ -1,7 +1,5 @@
 module.exports = {
   'rules': {
-    // disallow trailing commas in object literals
-    'comma-dangle': [2, 'always-multiline'],
     // disallow assignment in conditional expressions
     'no-cond-assign': [2, 'always'],
     // disallow use of console

packages/eslint-config-airbnb/rules/es6.js

@@ -30,6 +30,8 @@ module.exports = {
     // require space before/after arrow function's arrow
     // https://github.com/eslint/eslint/blob/master/docs/rules/arrow-spacing.md
     'arrow-spacing': [2, { 'before': true, 'after': true }],
+    // require trailing commas in multiline object literals
+    'comma-dangle': [2, 'always-multiline'],
     // verify super() callings in constructors
     'constructor-super': 0,
     // enforce the spacing around the * in generator functions

packages/eslint-config-airbnb/rules/legacy.js

@@ -1,5 +1,7 @@
 module.exports = {
   'rules': {
+    // disallow trailing commas in object literals
+    'comma-dangle': [2, 'never'],
     // specify the maximum depth that blocks can be nested
     'max-depth': [0, 4],
     // limits the number of parameters that can be used in the function declaration.