Update clause_specification_text.adoc

link to archived version of UncertML website (closed in 2016)

Author: chris-little

standard/clause_specification_text.adoc

@@ -989,7 +989,7 @@ In this example, extra attributes of the `Parameter` have been declared stating
     "label" : {
       "en": "Sea surface temperature daily mean"
     },
-    "statisticalMeasure": "http://www.uncertml.org/statistics/mean",
+    "statisticalMeasure": "https://web.archive.org/web/20161029215223/http://uncertml.org/statistics/mean",
     "narrower": ["http://vocab.nerc.ac.uk/standard_name/sea_surface_temperature/"]
   },
   "unit" : {