commit 86b5c4842a59f9b74d61a59a35ac303de778bf18
Author: Tom Hughes <tom@compton.nu>
Date:   Wed Oct 4 19:09:46 2017 +0100

    Update for mime 2.x

diff --git a/lib/render.js b/lib/render.js
index 24967eb..b70593e 100644
--- a/lib/render.js
+++ b/lib/render.js
@@ -173,7 +173,7 @@ MapnikSource.prototype._renderMetatile = function(options, callback) {
             options.headers = { 'Content-Type': 'image/jpeg' };
         } else {
             // will default to 'application/octet-stream' if unable to detect
-            options.headers = { 'Content-Type': mime.lookup(options.format.split(':')[0]) };
+            options.headers = { 'Content-Type': mime.getType(options.format.split(':')[0]) };
         }
         var image = new mapnik.Image(meta.width, meta.height);
     }