Use spock-main-logo.svg as favicon

Author: leonard84

spock-website/index.html

@@ -10,6 +10,7 @@
     <meta name="theme-color" content="#111827">
     <link rel="canonical" href="https://spockframework.org/">
     <meta name="robots" content="index, follow">
+    <link rel="icon" href="/spock-main-logo.svg" type="image/svg+xml">
 
     <meta property="og:type" content="website">
     <meta property="og:url" content="https://spockframework.org/">