Update context.jsonld (#16)

add missing commas

Author: chris-little

context.jsonld

@@ -53,9 +53,9 @@
     "parameters": { "@id": "covjson:parameter", "@type": "@id", "@container": "@index" },
 
     "observedProperty": "sosa:observedProperty",
-    "usedProcedure": "sosa:usedProcedure"
-    "madeBySensor": "sosa:madeBySensor"
-    "hasFeatureOfInterest": "sosa:hasFeatureOfInterest"
+    "usedProcedure": "sosa:usedProcedure",
+    "madeBySensor": "sosa:madeBySensor",
+    "hasFeatureOfInterest": "sosa:hasFeatureOfInterest",
 
     "categoryEncoding": "covjson:categoryEncoding",
     "ParameterGroup": "covjson:ParameterGroup",