scala – 使用sbt-assembly的assembly-merge-strategy问题

Merging 'org/apache/commons/logging/impl/SimpleLog.class' with strategy 'deduplicate'
    :assembly: deduplicate: different file contents found in the following:
    [error] /Users/home/.ivy2/cache/commons-logging/commons-logging/jars/commons-logging-1.1.1.jar:org/apache/commons/logging/impl/SimpleLog.class
    [error] /Users/home/.ivy2/cache/org.slf4j/jcl-over-slf4j/jars/jcl-over-slf4j-1.6.4.jar:org/apache/commons/logging/impl/SimpleLog.class

现在从sbt-assembly文档：

If multiple files share the same relative path (e.g. a resource named
application.conf in multiple dependency JARs),the default strategy is
to verify that all candidates have the same contents and error out
otherwise. This behavior can be configured on a per-path basis using
either one of the following built-in strategies or writing a custom one:

• MergeStrategy.deduplicate is the default described above
• MergeStrategy.first picks the first of the matching files in classpath order
• MergeStrategy.last picks the last one
• MergeStrategy.singleOrError bails out with an error message on conflict
• MergeStrategy.concat simply concatenates all matching files and includes the result
• MergeStrategy.filterDistinctLines also concatenates,but leaves out duplicates along the way
• MergeStrategy.rename renames the files originating from jar files
• MergeStrategy.discard simply discards matching files

通过这个我设置我的build.sbt如下：

import sbt._
import Keys._
import sbtassembly.Plugin._
import AssemblyKeys._
name := "my-project"
version := "0.1"
scalaVersion := "2.9.2"
crossScalaVersions := Seq("2.9.1","2.9.2")

//assemblySettings
seq(assemblySettings: _*)

resolvers ++= Seq(
    "Typesafe Releases Repository" at "http://repo.typesafe.com/typesafe/releases/","Typesafe Snapshots Repository" at "http://repo.typesafe.com/typesafe/snapshots/","Sonatype Repository" at "http://oss.sonatype.org/content/repositories/releases/"
)

libraryDependencies ++= Seq(
    "org.scalatest" %% "scalatest" % "1.6.1" % "test","org.clapper" %% "grizzled-slf4j" % "0.6.10","org.scalaz" % "scalaz-core_2.9.2" % "7.0.0-M7","net.databinder.dispatch" %% "dispatch-core" % "0.9.5"
)

scalacOptions += "-deprecation"
mainClass in assembly := Some("com.my.main.class")
test in assembly := {}
mergeStrategy in assembly := mergeStrategy.first

在build.sbt的最后一行，我有：

mergeStrategy in assembly := mergeStrategy.first

现在，当我运行SBT，我得到以下错误：

error: value first is not a member of sbt.SettingKey[String => sbtassembly.Plugin.MergeStrategy]
    mergeStrategy in assembly := mergeStrategy.first

有人可以指出我在这里做错什么？

谢谢