fix(valid-describe): allow concise body arrow function (#106)

Author: Saberre

Diff for: rules/__tests__/valid-describe.test.js

@@ -34,6 +34,11 @@ ruleTester.run('valid-describe', rule, {
       })
     })
     `,
+    `
+    describe('foo', () =>
+      test('bar', () => {})
+    )
+    `,
   ],
   invalid: [
     {

Diff for: rules/valid-describe.js

@@ -76,14 +76,16 @@ module.exports = {
               loc: paramsLocation(callbackFunction.params),
             });
           }
-          callbackFunction.body.body.forEach(node => {
-            if (node.type === 'ReturnStatement') {
-              context.report({
-                message: 'Unexpected return statement in describe callback',
-                node,
-              });
-            }
-          });
+          if (callbackFunction.body.type === 'BlockStatement') {
+            callbackFunction.body.body.forEach(node => {
+              if (node.type === 'ReturnStatement') {
+                context.report({
+                  message: 'Unexpected return statement in describe callback',
+                  node,
+                });
+              }
+            });
+          }
         }
       },
     };