Update open graph icon

Author: Emmanouil Konstantinidis

src/index.html

@@ -12,7 +12,7 @@
     <meta property="og:title" content="UIcolor.io" />
     <meta property="og:type" content="website" />
     <meta property="og:url" content="http://uicolor.io/" />
-    <meta property="og:image" content="http://uicolor.io/images/logo.svg" />
+    <meta property="og:image" content="http://uicolor.io/images/logo.png" />
     <meta property="og:description" content="UIColor is a website used to convert HEX & RGB colors to UIColor for both Objective-C and Swift featuring a colorpicker and copy to clipboard functionality making things easier." />
 
     <title>UI Color</title>