title: build.sbt breaks when adding spark-mllib
body: <p>I have the following in my build.sbt file:</p>
  
  <pre><code>import AssemblyKeys._
  
  assemblySettings
  
  name := "acme-get-flight-delays"
  version := "0.0.1"
  scalaVersion := "2.10.5"
  
  libraryDependencies ++= Seq(
    "org.apache.spark" %% "spark-hive" % "1.6.0",
    "org.scalanlp" %% "breeze" % "0.11.2",
    "net.liftweb" %% "lift-json" % "2.5+",
    "com.github.seratch" %% "awscala" % "0.3.+"
  )
  </code></pre>
  
  <p>and it builds just fine with <code>sbt assembly</code>.</p>
  
  <p>However, if I try to add</p>
  
  <pre><code>  "org.apache.spark" % "spark-mllib_2.11" % "1.6.2"
  </code></pre>
  
  <p>as a dependency, I get the following errors:</p>
  
  <pre><code>[error] Modules were resolved with conflicting cross-version suffixes in {file:/Users/paulreiners/dev/tv-insight-airport-delays/}tv-insight-airport-delays:
  [error]    org.apache.spark:spark-launcher _2.10, _2.11
  [error]    org.json4s:json4s-ast _2.10, _2.11
  [error]    org.apache.spark:spark-catalyst _2.10, _2.11
  [error]    org.apache.spark:spark-network-shuffle _2.10, _2.11
  [error]    com.typesafe.akka:akka-actor _2.10, _2.11
  [error]    com.twitter:chill _2.10, _2.11
  [error]    org.apache.spark:spark-sql _2.10, _2.11
  [error]    org.json4s:json4s-jackson _2.10, _2.11
  [error]    com.fasterxml.jackson.module:jackson-module-scala _2.10, _2.11
  [error]    org.scalanlp:breeze-macros _2.10, _2.11
  [error]    org.json4s:json4s-core _2.10, _2.11
  [error]    org.apache.spark:spark-unsafe _2.10, _2.11
  [error]    org.spire-math:spire _2.10, _2.11
  [error]    org.scalanlp:breeze _2.10, _2.11
  [error]    com.typesafe.akka:akka-remote _2.10, _2.11
  [error]    com.typesafe.akka:akka-slf4j _2.10, _2.11
  [error]    org.spire-math:spire-macros _2.10, _2.11
  [error]    org.apache.spark:spark-core _2.10, _2.11
  [error]    org.apache.spark:spark-network-common _2.10, _2.11
  java.lang.RuntimeException: Conflicting cross-version suffixes in: org.apache.spark:spark-launcher, org.json4s:json4s-ast, org.apache.spark:spark-catalyst, org.apache.spark:spark-network-shuffle, com.typesafe.akka:akka-actor, com.twitter:chill, org.apache.spark:spark-sql, org.json4s:json4s-jackson, com.fasterxml.jackson.module:jackson-module-scala, org.scalanlp:breeze-macros, org.json4s:json4s-core, org.apache.spark:spark-unsafe, org.spire-math:spire, org.scalanlp:breeze, com.typesafe.akka:akka-remote, com.typesafe.akka:akka-slf4j, org.spire-math:spire-macros, org.apache.spark:spark-core, org.apache.spark:spark-network-common
      at scala.sys.package$.error(package.scala:27)
      at sbt.ConflictWarning$.processCrossVersioned(ConflictWarning.scala:46)
      at sbt.ConflictWarning$.apply(ConflictWarning.scala:32)
      at sbt.Classpaths$$anonfun$69.apply(Defaults.scala:1219)
      at sbt.Classpaths$$anonfun$69.apply(Defaults.scala:1216)
      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:228)
      at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:228)
      at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:17)
      at sbt.Execute.work(Execute.scala:237)
      at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:228)
      at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:228)
      at sbt.ConcurrentRestrictions$$anon$4$$anonfun$1.apply(ConcurrentRestrictions.scala:159)
      at sbt.CompletionService$$anon$2.call(CompletionService.scala:28)
      at java.util.concurrent.FutureTask.run(FutureTask.java:266)
      at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
      at java.util.concurrent.FutureTask.run(FutureTask.java:266)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
      at java.lang.Thread.run(Thread.java:745)
  [error] (*:update) Conflicting cross-version suffixes in: org.apache.spark:spark-launcher, org.json4s:json4s-ast, org.apache.spark:spark-catalyst, org.apache.spark:spark-network-shuffle, com.typesafe.akka:akka-actor, com.twitter:chill, org.apache.spark:spark-sql, org.json4s:json4s-jackson, com.fasterxml.jackson.module:jackson-module-scala, org.scalanlp:breeze-macros, org.json4s:json4s-core, org.apache.spark:spark-unsafe, org.spire-math:spire, org.scalanlp:breeze, com.typesafe.akka:akka-remote, com.typesafe.akka:akka-slf4j, org.spire-math:spire-macros, org.apache.spark:spark-core, org.apache.spark:spark-network-common
  </code></pre>
  
  <p>What am I doing wrong here?</p>