fix exported classes with static class properties - fixes #2868

packages/babel-plugin-transform-class-properties/test/fixtures/general/static-undefined/actual.js

@@ -0,0 +1,3 @@
+class Foo {
+  static bar;
+}

packages/babel-plugin-transform-class-properties/test/fixtures/general/static-undefined/exec.js

@@ -0,0 +1,6 @@
+class Foo {
+  static num;
+}
+
+assert.equal("num" in Foo, false);
+assert.equal(Foo.num, undefined);

packages/babel-plugin-transform-class-properties/test/fixtures/general/static-undefined/expected.js

@@ -0,0 +1,3 @@
+var Foo = function Foo() {
+  babelHelpers.classCallCheck(this, Foo);
+};