Make formatter compatible with logrus >= 0.11.1
Make formatter compatible with logrus >= 0.11.1

- logrus made a breaking API change to `IsTerminal` function in
  https://github.com/sirupsen/logrus/pull/471/files that result in
  compilation error.
- this commit pretty much cherry-picks changes to `TextFormatter` from
  https://github.com/sirupsen/logrus/pull/471/files#diff-291b40d95620791b320dc56694c3a111

x-cray/logrus-prefixed-formatter