RtContents uses hardcoded master branch instead of default branch.

[volodya-lombrozo]

RtContents uses hardcoded master branch instead of default branch.
It could lead to some problems like that.

    @Override
    public Content get(
        final String path
    ) throws IOException {
        return this.content(path, "master");
    }

We can also replace all other similar places where we use "master" branch instead of default branch