[SPARK-959] Updated SBT from 0.13.1 to 0.13.2

JIRA issue: [SPARK-959](https://spark-project.atlassian.net/browse/SPARK-959)

SBT 0.13.2 has been officially released. This version updated Ivy 2.0 to Ivy 2.3, which fixes [IVY-899](https://issues.apache.org/jira/browse/IVY-899). This PR also removed previous workaround.

Author: Cheng Lian <lian.cs.zju@gmail.com>

Closes #426 from liancheng/updateSbt and squashes the following commits:

95e3dc8 [Cheng Lian] Updated SBT from 0.13.1 to 0.13.2 to fix SPARK-959

project/SparkBuild.scala

@@ -263,8 +263,6 @@ object SparkBuild extends Build {
         "org.eclipse.jetty" % "jetty-util"     % jettyVersion,
         "org.eclipse.jetty" % "jetty-plus"     % jettyVersion,
         "org.eclipse.jetty" % "jetty-security" % jettyVersion,
-        /** Workaround for SPARK-959. Dependency used by org.eclipse.jetty. Fixed in ivy 2.3.0. */
-        "org.eclipse.jetty.orbit" % "javax.servlet" % "3.0.0.v201112011016" artifacts Artifact("javax.servlet", "jar", "jar"),
         "org.scalatest"    %% "scalatest"       % "1.9.1"  % "test",
         "org.scalacheck"   %% "scalacheck"      % "1.10.0" % "test",
         "com.novocode"      % "junit-interface" % "0.10"   % "test",

project/build.properties

@@ -14,4 +14,4 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
-sbt.version=0.13.1
+sbt.version=0.13.2