no results for term surrounded by single quotes under Microsoft Windows 10

With

```vim
let g:grepper.prompt_quote = 2
```

under Windows 10, no results are found. That is, if the search term is surrounded by single quotes, then, under Windows 10, no grepper tool (be it git-grep, rg, ag, ...) finds any result.

Instead double quotes work fine.

Therefore

```vim
let g:grepper.prompt_quote = has('win32') ? 3 : 2
```

is to be recommended.

Search the plugin for g:grepper.prompt_quote and the command-building path used for git-grep, rg, ag, and other grep tools. Reproduce the single-quote search on Windows 10, then verify that the recommended Windows setting finds results while the non-Windows behavior and double-quoted searches remain correct.

Written by the indexing model from the issue text.