OpenIDConnect's New method returns "Provider, error" instead of just "Provider"

Nobody has claimed this yet.

For users of [Buffalo](https://github.com/gobuffalo/buffalo) along with the `openidConnect` provider, the default generated code will always contain an error. See this snippet:

```go
package actions

import (
"fmt"
"os"

"github.com/gobuffalo/buffalo"
"github.com/markbates/goth"
"github.com/markbates/goth/gothic"
"github.com/markbates/goth/providers/openidConnect"
)

func init() {
gothic.Store = App().SessionStore

goth.UseProviders(
openidConnect.New(os.Getenv("OPENIDCONNECT_KEY"), os.Getenv("OPENIDCONNECT_SECRET"), fmt.Sprintf("%s%s", App().Host, "/auth/openidconnect/callback"), "REDACT", "REDACT"),
)
}
```

The `goth.UseProviders` call expects *only* a `Provider` to be passed, but in the case of `openidConnect.New()`, we end up passing a `Provider` and `error` since that's what `openidConnect.New()` returns, so the code fails to compile.

One fix for this is to add a new function with a different name that's similar to the existing [`func New(clientKey, secret, callbackURL, openIDAutoDiscoveryURL string, scopes ...string) (*Provider, error)`](https://github.com/markbates/goth/blob/master/providers/openidConnect/openidConnect.go#L86), but that does not return an error (you could instead `panic`, or use some alternative way of dealing with the error).

That being said, I'd be happy to hear from anyone who has an alternative solution.

Start in providers/openidConnect/openidConnect.go at New and compare its return signature with the goth.UseProviders call shown in the issue. Review the generated Buffalo OpenID Connect setup and decide how the API should handle initialization errors; done means the generated setup can compile while retaining an explicit error-handling path.

Written by the indexing model from the issue text.