Re-added clearing of CollectorRegistry on startup to prevent problems…

… with registring exports when hot-reloading the app like when running Play via Sbt. Note that reloading does _not_ add the default exports since that class has an internal _initialized_ state which stays at _true_ when reloading classes preventing the exports to be added again.

app/com/github/stijndehaes/playprometheusfilters/PrometheusModule.scala

@@ -13,6 +13,8 @@ class PrometheusModule extends Module {
   import PrometheusModule._
 
   override def bindings(environment: Environment, configuration: Configuration): Seq[Binding[_]] = {
+    CollectorRegistry.defaultRegistry.clear()
+
     configuration.getOptional[Boolean](defaultExportsKey).foreach { enabled =>
       if (enabled) {
         DefaultExports.initialize()