Publish generated proto sources (#1328)

shared/javacpp/publish.gradle

@@ -20,6 +20,13 @@ task cppSourcesZip(type: Zip) {
     from('src/main/native/cpp') {
         into '/'
     }
+
+    // assume we will always have proto sources
+    from("$buildDir/generated/source/proto/main/cpp") {
+        into '/'
+    }
+
+    dependsOn generateProto
 }
 
 task cppHeadersZip(type: Zip) {