Avoid duplicates in importHints

src/app/compiler.js

@@ -223,9 +223,13 @@ function Compiler (editor, handleGithubCall) {
           if (importFilePath.startsWith('./')) {
             importFilePath = importFilePath.slice(2)
           }
+
+          // FIXME: should be using includes or sets, but there's also browser compatibility..
+          if (importHints.indexOf(importFilePath) === -1) {
             importHints.push(importFilePath)
           }
         }
+      }
       while (importHints.length > 0) {
         var m = importHints.pop()
         if (m in files) {