Fixes 1332

Skips warning on a single type declaration or type alias. Remove the check for `node.exportKind` as it is `undefined` in all test cases.

src/rules/prefer-default-export.js

@@ -47,8 +47,9 @@ module.exports = {
         // if there are specifiers, node.declaration should be null
         if (!node.declaration) return
 
-        // don't count flow types exports
-        if (node.exportKind === 'type') return
+        // don't warn on single type aliases or declarations
+        if(node.declaration.type === 'TSTypeAliasDeclaration'
+          || node.declaration.type === 'TypeAlias') return
 
         if (node.declaration.declarations) {
           node.declaration.declarations.forEach(function(declaration) {

tests/src/rules/prefer-default-export.js

@@ -84,6 +84,16 @@ ruleTester.run('prefer-default-export', rule, {
       parser: 'babel-eslint',
     }),
 
+    // Single type declaration
+    test({
+      code: 'export type foo = string',
+      parser: 'typescript-eslint-parser',
+    }),
+    test({
+      code: 'export type foo = string',
+      parser: 'babel-eslint',
+    }),
+
     // ...SYNTAX_CASES,
   ],
   invalid: [