fix partly rendered search preview

[thisconnect]

The preview in search results dropdown showed sometimes jekyll includes when it should display text snippets of the results.

The problem is when search-data.json is rendered every file after S has not been rendered yet as jekyll processes all files in alphabetical order. In that case the search might display jekyll includes or raw markdown.

Renaming search-data.json to zzzz-search-data with a permalink fixes this, see upstream fix. Also removed .json as the file is a template that will render to JSON.

https://github.com/pmarsceill/just-the-docs/issues/191#issuecomment-557836956

[thisconnect]

i.e. search for "pending"

Before:

After:

[jstrnbrg]

tested, LGTM @thisconnect