switched nedb to nedb-promises (#37)

* breaking change: switched to nedb-promises
* Linting
* some dev dependencies
* more tests
* updated package version
* bug fixing
* changed isNaN to isString
* (fix) args[0]

__tests__/functions/isEmpty.js

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