v1.2.1 修复1-99年日期错乱的问题；增加单元测试。

__tests__/SolarHalfYear.test.js

@@ -0,0 +1,13 @@
+var {SolarHalfYear} = require('../lunar');
+
+test('toString()', () => {
+  const halfYear = SolarHalfYear.fromYm(2019, 5);
+  expect(halfYear.toString()).toBe('2019.1');
+  expect(halfYear.next(1).toString()).toBe('2019.2');
+});
+
+test('toFullString()', () => {
+  const halfYear = SolarHalfYear.fromYm(2019, 5);
+  expect(halfYear.toFullString()).toBe('2019年上半年');
+  expect(halfYear.next(1).toFullString()).toBe('2019年下半年');
+});