Upgrade to gradle 4.8.1

dd-trace-java.gradle

@@ -53,7 +53,7 @@ buildScan {
   }
 }
 
-ext.gradleWrapperVersion = '4.7'
+ext.gradleWrapperVersion = '4.8.1'
 task wrapper(type: Wrapper) {
   gradleVersion = gradleWrapperVersion
 }

dd-trace-ot/src/test/groovy/datadog/trace/api/writer/DDApiTest.groovy

@@ -20,7 +20,6 @@ import static ratpack.groovy.test.embed.GroovyEmbeddedApp.ratpack
 class DDApiTest extends Specification {
   static mapper = new ObjectMapper(new MessagePackFactory())
 
-  // first test takes longer
   def "sending an empty list of traces returns no errors"() {
     setup:
     def agent = ratpack {

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.7-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.8.1-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists