Fix opening links containing ampersands (&) in WSL

Opening links containing ampersands inside lazygit (a pull-request
creation page in BitBucket Server, for instance) returns the following
Powershell error:
> The ampersand (&) character is not allowed. The & operator is reserved
> for future use; wrap an ampersand in double quotation marks ("&") to
> pass it as part of a string.

We fix it by enclosing the URL in single quotes.

pkg/config/config_linux.go

@@ -22,7 +22,7 @@ func GetPlatformDefaultConfig() OSConfig {
 	if isWSL() && !isContainer() {
 		return OSConfig{
 			Open:     `powershell.exe start explorer.exe "$(wslpath -w {{filename}})" >/dev/null`,
-			OpenLink: `powershell.exe start {{link}} >/dev/null`,
+			OpenLink: `powershell.exe start '{{link}}' >/dev/null`,
 		}
 	}