Fixed slack unfurl image (#655)

Author: sriumcp

mkdocs/overrides/main.html

@@ -31,15 +31,15 @@
   <meta property="og:title" content="The Kubernetes experimentation platform" />
   <meta property="og:description" content="{{ config.site_description }}" />
   <meta property="og:url" content="https://iter8.tools" />
-  <meta property="og:image" content="https://iter8.tools/0.4/images/illustration.png" />
+  <meta property="og:image" content="https://iter8.tools/0.5/images/illustration.png" />
 
   <!-- Twitter meta tags -->
   <meta name="twitter:card" content="summary_large_image" />
   <meta name="twitter:url" content="https://iter8.tools" />
   <meta name="twitter:creator" content="{{ config.site_author }}" />
   <meta name="twitter:title" content="The Kubernetes experimentation platform" />
   <meta name="twitter:description" content="{{ config.site_description }}" />
-  <meta name="twitter:image" content="https://iter8.tools/0.4/images/illustration.png" />
+  <meta name="twitter:image" content="https://iter8.tools/0.5/images/illustration.png" />
   <meta name="twitter:label1" value="Experiments" />
   <meta name="twitter:data1" value="A/B, A/B/n, Canary, Conformance" />
   <meta name="twitter:label2" value="K8s stacks" />