Defining `edit_uri` as anything other than an empty string modifies the `repo_url`

### Description

Defining `edit_uri` as anything other than an empty string adds a forward slash to the `repo_url` link for the button on the top right

### Expected behavior

The `repo_url` link for the button on the top right is what is defined in config

### Versions

- Python: `3.8.1`
- MkDocs: `1.2.3`

### System information

- Operating system: Windows 10
- Browser: Chrome