Add scala 2.13 cross build

Author: note

build.sbt

@@ -1,7 +1,8 @@
 name := "scala-lambda-handler"
 organization := "com.lifeway.aws"
 
-scalaVersion := "2.12.8"
+scalaVersion := "2.13.1"
+crossScalaVersions := Seq("2.12.11", "2.13.1")
 
 val circeVersion = "0.12.3"
 val slf4jVersion = "1.7.26"
@@ -12,7 +13,7 @@ libraryDependencies ++= Seq(
   "org.slf4j"     % "slf4j-api"            % slf4jVersion,
   "com.amazonaws" % "aws-lambda-java-core" % "1.2.0",
   "com.lihaoyi"   %% "requests"            % "0.2.0",
-  "com.lihaoyi"   %% "utest"               % "0.6.3" % "test"
+  "com.lihaoyi"   %% "utest"               % "0.7.4" % "test"
 )
 
 testFrameworks += new TestFramework("utest.runner.Framework")

project/build.properties

@@ -1 +1 @@
-sbt.version=1.1.1
+sbt.version=1.3.8

project/plugins.sbt

@@ -1,4 +1,4 @@
-addSbtPlugin("org.scoverage"     % "sbt-scoverage" % "1.5.1")
+addSbtPlugin("org.scoverage"     % "sbt-scoverage" % "1.6.1")
 addSbtPlugin("com.jsuereth"      % "sbt-pgp"       % "1.1.0")
 addSbtPlugin("org.xerial.sbt"    % "sbt-sonatype"  % "2.3")
 addSbtPlugin("com.github.gseitz" % "sbt-release"   % "1.0.7")

src/main/scala/com/lifeway/aws/lambda/ProxyWithBody.scala

@@ -5,6 +5,7 @@ import com.amazonaws.services.lambda.runtime.Context
 import io.circe
 import io.circe._
 import io.circe.parser._
+import com.lifeway.aws.lambda.Errors
 
 /**
   * Abstract Lambda Handler for Scala for API Gateway Proxied requests containing a JSON message body. You must extend

src/test/scala/com/lifeway/aws/lambda/ErrorsTest.scala

@@ -1,5 +1,6 @@
 package com.lifeway.aws.lambda
 
+import com.lifeway.aws.lambda.Errors
 import io.circe._
 import io.circe.syntax._
 import utest._

src/test/scala/com/lifeway/aws/lambda/ProxyNoBodyTest.scala

@@ -1,5 +1,6 @@
 package com.lifeway.aws.lambda
 
+import com.lifeway.aws.lambda.Errors
 import java.io.ByteArrayOutputStream
 
 import com.amazonaws.services.lambda.runtime.Context

src/test/scala/com/lifeway/aws/lambda/ProxyWithBodyTest.scala

@@ -1,5 +1,6 @@
 package com.lifeway.aws.lambda
 
+import com.lifeway.aws.lambda.Errors
 import java.io.ByteArrayOutputStream
 
 import com.amazonaws.services.lambda.runtime.Context