[BUILD] Fixed resolver for scalastyle plugin and upgrade sbt version.

Author: Prashant Sharma <prashant.s@imaginea.com>

Closes #2877 from ScrapCodes/scalastyle-fix and squashes the following commits:

a17b9fe [Prashant Sharma] [BUILD] Fixed resolver for scalastyle plugin.

project/build.properties

@@ -14,4 +14,4 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
-sbt.version=0.13.5
+sbt.version=0.13.6

project/plugins.sbt

@@ -4,6 +4,8 @@ resolvers += Resolver.url("artifactory", url("http://scalasbt.artifactoryonline.
 
 resolvers += "Typesafe Repository" at "http://repo.typesafe.com/typesafe/releases/"
 
+resolvers += "sonatype-releases" at "https://oss.sonatype.org/content/repositories/releases/"
+
 addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.11.2")
 
 addSbtPlugin("com.typesafe.sbteclipse" % "sbteclipse-plugin" % "2.2.0")