Vue Scroll Versions Save

1. Fixed this issue: https://github.com/wangpin34/vue-scroll/issues/35
2. Move demo to codesandbox

Fixed:

• https://github.com/wangpin34/vue-scroll/issues/32

Lodash optimization https://github.com/wangpin34/vue-scroll/pull/31

Add umd, commonjs, es6 pkg for dist

v2.1.0 is comming with more powerful features

• Throttle
• Debounce

Fix non-block bugs

Fix a bug. The older doesn's support replace scroll listener well.