Use instance/test until negative fields bug in virtual corpora is fixed in main instance

See https://korap.ids-mannheim.de/gerrit/#/c/KorAP/Krill/+/2338/

Change-Id: Ibe741947675f1c241b8270177e9054bf86b81ca1
diff --git a/R/KorAPConnection.R b/R/KorAPConnection.R
index 84aec06..099975c 100644
--- a/R/KorAPConnection.R
+++ b/R/KorAPConnection.R
@@ -28,7 +28,7 @@
 #' @rdname KorAPConnection-class
 #' @export
 setMethod("initialize", "KorAPConnection",
-          function(.Object, KorAPUrl = "https://korap.ids-mannheim.de/", apiVersion = 'v1.0', apiUrl) {
+          function(.Object, KorAPUrl = "https://korap.ids-mannheim.de/instance/test/", apiVersion = 'v1.0', apiUrl) {
             .Object <- callNextMethod()
             m <- regexpr("https?://[^?]+", KorAPUrl, perl = TRUE)
             .Object@KorAPUrl <- regmatches(KorAPUrl, m)