Update index.html (#858)

correct spelling

examples/index.html

@@ -15,7 +15,7 @@
       <p>
         <a href="https://github.com/ArthurSonzogni/FTXUI">FTXUI</a> is a simple
         functional C++ library for terminal user interface. <br/>
-        This showcase the: <a href="https://github.com/ArthurSonzogni/FTXUI/tree/master/examples">./example/</a> folder. <br/>
+        This showcases the: <a href="https://github.com/ArthurSonzogni/FTXUI/tree/master/examples">./example/</a> folder. <br/>
       </p>
 
       <div id="terminalContainer">