Add placeholder logo for opengraph

Task #212

Author: cmaureir

src/config/config.json

@@ -19,7 +19,7 @@
 
   "metadata": {
     "meta_author": "Themefisher modified by PyLadiesCon",
-    "meta_image": "/images/og-image.png",
+    "meta_image": "/images/logo.svg",
     "meta_description": "PyLadiesCon Blog & Documentation"
   },