[Windows] [ssh-runner] Powershell Env Escaping

Env var escaping in Powershell is broken with the SSH Runner:

If I use quotes in a commit message like

"fix" bug

The build will fail with an error like this:

$Env:DRONE_COMMIT_MESSAGE = "\"fix\" bug\n"
 Unexpected token 'fix\" bug\n"' in expression or statement.
    + CategoryInfo          : ParserError: (:) [], ParentContainsErrorRecordException
    + FullyQualifiedErrorId : UnexpectedToken

it should be

$Env:DRONE_COMMIT_MESSAGE = "`"fix`" bug\n"


the escaping logic can be found at https://github.com/drone/runner-go/blob/master/shell/powershell/powershell.go#L29