Tweak: Add --all to !List command (#39)

* tweaked on list command

* added more tests

__tests__/functions/isString.js

@@ -0,0 +1,12 @@
+require('module-alias/register');
+const { isString } = require('@dsabot/isString');
+
+it('should return true statements', () => {
+    expect(isString({})).toBeFalsy();
+    expect(isString()).toBeFalsy();
+    expect(isString('')).toBeTruthy();
+    expect(isString([])).toBeFalsy();
+    expect(isString({ key: 'value' })).toBeFalsy();
+    expect(isString([null])).toBeFalsy();
+    expect(isString([''])).toBeFalsy();
+});