Build: Fix artifacts signing for maven central

With gradle > 5.0 `publish()` helper call should be done before
`noDefaultJar()` or any other artifact hacks, otherwise singing plugin doesn't sign any jars

libraries/tools/kotlin-gradle-plugin-model/build.gradle.kts

@@ -6,9 +6,10 @@ plugins {
     maven
 }
 
-standardPublicJars()
 publish()
 
+standardPublicJars()
+
 dependencies {
     compile(kotlinStdlib())
 }