Fix not working with our OSS publish pipeline. (#3)

Need to include the nexus publishing plugin.

Author: JonathanO

build.gradle

@@ -5,6 +5,7 @@ plugins {
     id 'com.google.protobuf' version '0.8.18'
     id 'idea'
     id 'org.ajoberstar.grgit' version '4.1.1'
+    id 'io.github.gradle-nexus.publish-plugin' version "1.1.0"
 }
 
 group = "com.transferwise.envoy"
@@ -76,6 +77,15 @@ apply plugin: "signing"
 ext.artifactoryUser = project.hasProperty("artifactoryUser") ? project.artifactoryUser : System.env.ARTIFACTORY_USER as String
 ext.artifactoryPassword = project.hasProperty("artifactoryPassword") ? project.artifactoryPassword : System.env.ARTIFACTORY_PASSWORD as String
 
+nexusPublishing {
+    repositories {
+        sonatype {
+            username = System.getenv("SONATYPE_USER")
+            password = System.getenv("SONATYPE_PASSWORD")
+        }
+    }
+}
+
 publishing {
     publications {
         mavenJava(MavenPublication) {