Fix Thrift benchmark for Scala 2.11

[travisbrown]

Currently the Thrift benchmark crashes SBT with the following error on 2.11 (2.10 works just fine):

Annotation generator had thrown the exception.
java.lang.IncompatibleClassChangeError: i.g.f.s.thriftscala.Small and i.g.f.s.thriftscala.Small$Proxy$class disagree on InnerClasses attribute
        at java.lang.Class.getDeclaringClass0(Native Method)
        at java.lang.Class.getDeclaringClass(Class.java:1106)
        at java.lang.Class.getEnclosingClass(Class.java:1142)
        at java.lang.Class.getCanonicalName(Class.java:1231)
        at org.openjdk.jmh.generators.reflection.RFClassInfo.getQualifiedName(RFClassInfo.java:67)
        at org.openjdk.jmh.generators.core.BenchmarkGenerator.buildAnnotatedSet(BenchmarkGenerator.java:213)
        at org.openjdk.jmh.generators.core.BenchmarkGenerator.generate(BenchmarkGenerator.java:108)
        at org.openjdk.jmh.generators.bytecode.JmhBytecodeGenerator.main(JmhBytecodeGenerator.java:100)
        at pl.project13.scala.sbt.SbtJmh$.generateBenchmarkJavaSources(SbtJmh.scala:81)
        at pl.project13.scala.sbt.SbtJmh$$anonfun$jmhSettings$6.apply(SbtJmh.scala:28)
        at pl.project13.scala.sbt.SbtJmh$$anonfun$jmhSettings$6.apply(SbtJmh.scala:28)
        at scala.Function1$$anonfun$compose$1.apply(Function1.scala:47)
        at sbt.$tilde$greater$$anonfun$$u2219$1.apply(TypeFunctions.scala:40)
        at sbt.std.Transform$$anon$4.work(System.scala:63)
        at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:226)
        at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:226)
        at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:17)
        at sbt.Execute.work(Execute.scala:235)
        at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:226)
        at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:226)
        at sbt.ConcurrentRestrictions$$anon$4$$anonfun$1.apply(ConcurrentRestrictions.scala:159)
        at sbt.CompletionService$$anon$2.call(CompletionService.scala:28)
        at java.util.concurrent.FutureTask.run(FutureTask.java:262)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
        at java.util.concurrent.FutureTask.run(FutureTask.java:262)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:745)

Probably a Scrooge problem, but needs more investigation.