Fix bug 1527

Move from xip.io to nip.io

Change-Id: Id861f8dac7c38786544383985a1a75cf0bce16df
Signed-off-by: David Garcia <david.garcia@canonical.com>
diff --git a/installers/charm/prometheus/tests/test_charm.py b/installers/charm/prometheus/tests/test_charm.py
index 0713a84..66e199d 100644
--- a/installers/charm/prometheus/tests/test_charm.py
+++ b/installers/charm/prometheus/tests/test_charm.py
@@ -44,7 +44,7 @@
             "max_file_size": 0,
             "ingress_whitelist_source_range": "",
             "tls_secret_name": "",
-            "site_url": "https://prometheus.192.168.100.100.xip.io",
+            "site_url": "https://prometheus.192.168.100.100.nip.io",
             "cluster_issuer": "vault-issuer",
             "enable_web_admin_api": False,
         }