Use str.format for the demo

wasm/demo/src/index.html

@@ -19,7 +19,7 @@ n2 = 1
 count = 0
 until = 10
 
-print("These are the first " + str(until) + " number in a Fibonacci sequence:")
+print("These are the first {} numbers in a Fibonacci sequence:".format(until))
 
 while count < until:
     print(n1)