Allow for easier debugging

Currently, we won't see any stack trace in the error output, e.g. while
diagnosing the problem we encountered in
git-for-windows/build-extra#455 (comment).

Let's make that easier to pinpoint.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

GitForWindowsHelper/index.js

@@ -27,6 +27,7 @@ module.exports = async function (context, req) {
             && req.body.comment?.body
             && req.body.comment.body.startsWith('/')) return ok(await slashCommand(context, req))
     } catch (e) {
+        context.log(e)
         return withStatus(500, undefined, e.toString('utf-8'))
     }