Support detecting .lgtm file inside .github folder

[tasomaniac]

Github has now supporting .github folder for these kind of configuration. Issue and PR templates are detected if they are in .github folder.

LGTM can do the same too.

[bradrydzewski]

I recommend altering the following function [1] to accept a list of files:

-GetContents(*model.User, *model.Repo, string) ([]byte, error)
+GetContents(*model.User, *model.Repo, string...) ([]byte, error)

This function would then return the first file in the list it is able to successfully download. We could then specify [2] multiple configuration files paths including in the .github directory:

-GetContents(c, user, repo, ".lgtm") ([]byte, error)
+GetContents(c, user, repo, ".lgtm", ".github/.lgtm") ([]byte, error)

This change shouldn't be too difficult, however, I have other priorities and am therefore marking this issue as help wanted. If anyone is interested in sending a pull request let me know!

[1] https://github.com/lgtmco/lgtm/blob/master/remote/remote.go#L45
[2] https://github.com/lgtmco/lgtm/blob/master/web/hook.go#L40