Update contributors.js for better performance

append element to the DOM too many times may cause performance issue,
so do it only once.

js/contributors.js

@@ -3,12 +3,14 @@ function getContributors() {
     const container = $('#contributors');
     jQuery.ajax('https://api.github.com/repos/mikebryant/ac-nh-turnip-prices/contributors', {})
       .done(function (data) {
+        const contributorList = [];
         data.forEach((contributor, idx) => {
-          container.append(`<a href="${contributor.html_url}">${contributor.login}</a>`);
+          contributorList.push(`<a href="${contributor.html_url}">${contributor.login}</a>`);
           if (idx < data.length - 1) {
-            container.append(', ');
+            contributorList.push(', ');
           }
         });
+        container.append(contributorList.join(''));
       });
   }
 }