fix typo in website (#476)

web/templates/index.html

@@ -18,7 +18,7 @@ <h1>Features</h1>
             <div class="content">
                 <h2>Composable</h3>
                 Filament uses a new kind of type system to ensure that when you use a module to perform a computation,
-                it's timing constraints, like latency and initiation interval are correct. When there are errors, it
+                its timing constraints, like latency and initiation interval are correct. When there are errors, it
                 generates helpful error messages to explain what is wrong with the design!
             </div>
         </div>