Update produced malformed code

[fthomas]

see https://github.com/maximn/TaxCalculator/pull/1/files

The diff is:

- libraryDependencies ++= Seq("org.specs2" %% "specs2-core" % "3.+" % "test")
+ libraryDependencies ++= Seq("org.specs2" %% "specs2-core" % "4.3.4