fix(theme-default): include path in sidebar heading links

[kvanzuijlen]

Before submitting the PR, please make sure you do the following

• [x] Read the Contributing Guidelines.
• [x] Provide a description in this PR that addresses what the PR is solving. If this PR is going to solve an existing issue, please reference the issue (e.g. close #123).

What is the purpose of this pull request?

• [x] Bug fix
• [ ] New feature
• [ ] Other

Description

This PR fixes a bug/oversight that caused paths not to be included in the links to headers in the sidebar. Closes #81

Screenshots

Before

After

[Mister-Hope]

The issue should be an / placed before the anchor, and that should be a issue with core, I refuse a workaround like this.

[kvanzuijlen]

I think the changes to isActiveSidebarItem would still be required when this gets solved in vuepress/core though, right?

[Mister-Hope]

No, we perfer a clean anchor rather than a full link. Its just a / is placed before the # by mistake.

[kvanzuijlen]

Ah yes, you're right! I'll try to look into that when I find some time!