Issue title: SourceForge issues: Hash check failed for *
 Issue body: Installing 'innounp' (0.46).
innounp046.rar (652 B) [======================================================================================] 100%
Checking hash of innounp046.rar... Hash check failed for 'https://sourceforge.net/projects/innounp/files/innounp/innounp%200.46/innounp046.rar/'.
Expected:
    3c056e2fc46ca9e92405f13ddf1f250cfe4bd66cb83b6647d87c74bc7242b121
Actual:
    7a07d3f7cca5c0b38ca811984ef8da536da32932d68c1a6cce33ec2462b930bf
 Comments: 
 Comment 0: Execute `scoop cache rm innounp` to clean cache then try to install it again.
 Comment 1: @h404bi Does installing innounp work for you?
I'm on a completely clean machine so innounp isn't in the cache (it also doesn't end up there if hash check fails)
 Comment 2: * SourceForge is experiencing connectivity issues. See: https://twitter.com/sfnet_ops
* Please follow the steps @h404bi mentioned when those issues got fixed by SourceForge.
  * Execute `scoop cache rm <app>` to clean the cache
  * Then try to install the program again
 Comment 3: @cholmquist Maybe you got redirected to a broken SF.net mirror, see #1732 and #1731
 Comment 4: Changing the title so others with the same problem can report to this issue.
 Comment 5: Thanks guys, that explained the problem.

If I'm using a browser to navigate to https://sourceforge.net/projects/innounp/files/innounp/innounp%200.46/innounp046.rar
I get this response
"The sourceforge.net website is temporarily in static offline mode"

This links seems to work though
https://downloads.sourceforge.net/project/innounp/innounp/innounp%200.46/innounp046.rar

 Comment 6: Noticing the same issue over here. Tried `scoop cache rm innounp` and reinstalling, still supposedly having a Hash check.
 Comment 7: This appears to be resolved. If not, let us know. Thanks.
 Comment 8: I still occasionally see scoop downloading the sourceforge project's download page instead of the actual file. As I write this, it's doing it for filezilla:

```
FileZilla_3.31.0_win64.zip (244.9 KB) [=======================================================================================================================================================] 100%
```

```powershell
PS> sls '<title>' .\filezilla#3.31.0#https_sourceforge.net_projects_filezilla_files_FileZilla_Client_3.31.0_FileZilla_3.31.0_win64.zip | % Line | % Trim

<title>Download FileZilla® from SourceForge.net</title>
```

It's especially annoying since the `current` junction and the .exe shim get deleted despite the hash check failure, and it's non-trivial to recover.

I've switched back to chocolatey for anything that scoop downloads from sourceforge. As annoying as chocolatey is in comparison to scoopy, atleast it *works*.
 Comment 9: Agreed. We should not be uninstalling an app prior to checking the hash matches.
 Comment 10: Here’s a thought: we add a `mirrors.json`:
```
{
 “https://sourceforge.net/projects/$project/files/”:
    “https://sourceforge.mirrorservice.org/$project[0]/$project[0]$project[1]/$project/“,
 “https://downloads.sourceforge.net/project/$project/“:
    “https://sourceforge.mirrorservice.org/$project[0]/$project[0]$project[1]/$project/“,
...
}
```
And if a hash check fails, we try a mirror before giving up.
{'source': 'GithubIssues', 'repo_name_with_owner': 'ScoopInstaller/Scoop', 'issue_id': 261053717, 'repo_stars': 16487.0}