Update Twitter Util to 7.1.0 (and switch to SBT 1.0)

[travisbrown]

These should be separate PRs but I'm in a hurry. I've removed WartRemover because I've never really found it useful for this project and it's not available for SBT 1.0.

Of course the SBT upgrade breaks random stuff (in this case incremental compilation, apparently): if you check out 60ac81d, build, then check out 132b612 and build again, you get this error:

[error] Symbol 'type io.catbird.finagle.ServiceInstances' is missing from the classpath.
[error] This symbol is required by 'package io.catbird.finagle.package'.
[error] Make sure that type ServiceInstances is in your classpath and check for conflicting dependencies with `-Ylog-classpath`.
[error] A full rebuild may help if 'package.class' was compiled against an incompatible version of io.catbird.finagle.
[error] one error found

Cleaning fixes it, and I don't really care enough to try to figure out why it's happening.

[codecov-io]

Codecov Report

Merging #47 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #47   +/-   ##
=======================================
  Coverage   65.61%   65.61%           
=======================================
  Files          12       12           
  Lines         253      253           
  Branches        2        2           
=======================================
  Hits          166      166           
  Misses         87       87

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