Update index.html

Added missing target in markup

Author: Gmac4247

index.html

@@ -400,6 +400,7 @@
        "name":"Surface area of a cone",
        "description": "The exact surface area of a cone based on its radius and height.",
      "disambiguatingDescription": "Based on the real height.",
+	"target": "https://basic-geometry.github.io",
 	"mathExpression-input": "required cone_radius=5_height=3_Area=?",
      "mathExpression-output": "Area = 3.2 * radius * (radius + sqrt(radius^2 +height^2))", 
     "about": "The bottom of a cone is a circle. The rest of its surface can be calculated as a circle slice.",