fix(demo): downgrade docsify to specify version

[scplay]

downgrade docsify make it compatible with vuep to show v-chart demo

Not sure what change cause issue.

Here is reference diff for the version which not work since 4.12.0 (release Note) compare to 4.11.6 (work well with vuep)

Check List

• [x] Every Commit message is meaningful
• [ ] Synchronized with the master branch
• [ ] CI passed

What Changed

Breaking Change

• [ ] Yes
• [x] No

Document Update

• [x] Yes
• [ ] No