v1.2.1 修复1-99年日期错乱的问题；增加单元测试。

__tests__/SolarMonth.test.js

@@ -0,0 +1,13 @@
+var {SolarSeason} = require('../lunar');
+
+test('toString()', () => {
+  const season = SolarSeason.fromYm(2019, 5);
+  expect(season.toString()).toBe('2019.2');
+  expect(season.next(1).toString()).toBe('2019.3');
+});
+
+test('toFullString()', () => {
+  const season = SolarSeason.fromYm(2019, 5);
+  expect(season.toFullString()).toBe('2019年2季度');
+  expect(season.next(1).toFullString()).toBe('2019年3季度');
+});