Make fetchMediumJSON's URL guessing more intelligent

Now, it checks and processes the current query string instead of
blindly tacking on a "?format=json" at the end.

seance.js

@@ -336,9 +336,19 @@ class Seance {
     var text
 
     if (mediumUrl.match(/^http/i)) {
-      // add ?json attribute
+      // remove the anchors at the end
       mediumUrl = mediumUrl.replace(/#.*$/, '')
+
+      // intelligently add ?json attribute
+      if (mediumUrl.indexOf('format=json') == -1) {
+        if (mediumUrl.indexOf('?') == 0) {
           mediumUrl = `${mediumUrl}?format=json`
+        } else {
+          mediumUrl = `${mediumUrl}&format=json`
+        }
+      }
+
+      // let's get it!
       const response = await fetch(mediumUrl)
       text = await response.text()
     } else if (fs.existsSync(mediumUrl)) {