fixed body of sensors_api.md

sensors_api.md

@@ -17,7 +17,7 @@ Variables are defined as **${variable_name}**
     { 
       "n": "Temperature", // name of the quantity 
       "v": "10", // value
-      "u": "°C" // unit
+      "u": "°C", // unit
       "d": "Int32" // data type
     }
    ]