Fix/unresponsive sponsorship images in smaller screens (#454)

* adjusted sponsors image logos for smaller screens

* Linting tests passing

Author: TimOsahenru

assets/css/bpd.css

@@ -510,3 +510,10 @@ ul.speaking-list {
   width: 100%;
   height: 100%;
 }
+
+/* Adjust sponsors images on smaller screens */
+@media (max-width: 600px) {
+  .grid img {
+    max-width: 60%;
+  }
+}