diff --git a/package.json b/package.json
index 80ae39f9..8c38e659 100644
--- a/package.json
+++ b/package.json
@@ -51,7 +51,7 @@
     "mkdirp": "^0.5.1",
     "pako": "1.0.6",
     "postcss-loader": "^3.0.0",
-    "query-string": "^6.1.0",
+    "query-string": "^5.1.1",
     "rimraf": "^2.6.2",
     "rollup": "^0.63.4",
     "rollup-plugin-babel": "^3.0.7",
diff --git a/website/static/js/scrollspy.js b/website/static/js/scrollspy.js
index 0b2987c2..da6bddc3 100644
--- a/website/static/js/scrollspy.js
+++ b/website/static/js/scrollspy.js
@@ -1,26 +1,31 @@
+/* eslint-disable no-var */
 // Inspired by ScrollSpy as in e.g. Bootstrap
 
 (function() {
-    const OFFSET = 10;
-    let timer;
-    let headingsCache;
-    const findHeadings = () => headingsCache ? headingsCache :
-        document.querySelectorAll('.toc-headings > li > a');
-    const onScroll = () => {
+    var OFFSET = 10;
+    var timer;
+
+    var headingsCache;
+    function findHeadings() {
+        return headingsCache ? headingsCache :
+            document.querySelectorAll('.toc-headings > li > a');
+    }
+
+    function onScroll() {
         if (timer) {  // throttle
             return;
         }
-        timer = setTimeout(() => {
+        timer = setTimeout(function() {
             timer = null;
-            let found = false;
-            const headings = findHeadings();
-            for (let i = 0; i < headings.length; i++) {
+            var found = false;
+            var headings = findHeadings();
+            for (var i = 0; i < headings.length; i++) {
                 // if !found and i is the last element, highlight the last
-                let current = !found;
+                var current = !found;
                 if (!found && i < headings.length - 1) {
-                    const next = headings[i + 1].href.split('#')[1];
-                    const nextHeader = document.getElementById(next);
-                    const top = nextHeader.getBoundingClientRect().top;
+                    var next = headings[i + 1].href.split('#')[1];
+                    var nextHeader = document.getElementById(next);
+                    var top = nextHeader.getBoundingClientRect().top;
                     // The following tests whether top + scrollTop
                     // (the top of the header) is greater than scrollTop
                     // (where scrollTop = window.pageYOffset, the top of
@@ -35,10 +40,11 @@
                 }
             }
         }, 100);
-    };
+    }
+
     document.addEventListener('scroll', onScroll);
     document.addEventListener('resize', onScroll);
-    document.addEventListener('DOMContentLoaded', () => {
+    document.addEventListener('DOMContentLoaded', function() {
         // Cache the headings once the page has fully loaded.
         headingsCache = findHeadings();
         onScroll();
diff --git a/yarn.lock b/yarn.lock
index a5720a6b..c02a7a9a 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -5958,12 +5958,13 @@ qs@~6.5.1:
   version "6.5.2"
   resolved "https://registry.yarnpkg.com/qs/-/qs-6.5.2.tgz#cb3ae806e8740444584ef154ce8ee98d403f3e36"
 
-query-string@^6.1.0:
-  version "6.1.0"
-  resolved "https://registry.yarnpkg.com/query-string/-/query-string-6.1.0.tgz#01e7d69f6a0940dac67a937d6c6325647aa4532a"
+query-string@^5.1.1:
+  version "5.1.1"
+  resolved "https://registry.yarnpkg.com/query-string/-/query-string-5.1.1.tgz#a78c012b71c17e05f2e3fa2319dd330682efb3cb"
   dependencies:
     decode-uri-component "^0.2.0"
-    strict-uri-encode "^2.0.0"
+    object-assign "^4.1.0"
+    strict-uri-encode "^1.0.0"
 
 querystring-es3@^0.2.0:
   version "0.2.1"
@@ -6879,9 +6880,9 @@ stream-shift@^1.0.0:
   version "1.0.0"
   resolved "https://registry.yarnpkg.com/stream-shift/-/stream-shift-1.0.0.tgz#d5c752825e5367e786f78e18e445ea223a155952"
 
-strict-uri-encode@^2.0.0:
-  version "2.0.0"
-  resolved "https://registry.yarnpkg.com/strict-uri-encode/-/strict-uri-encode-2.0.0.tgz#b9c7330c7042862f6b142dc274bbcc5866ce3546"
+strict-uri-encode@^1.0.0:
+  version "1.1.0"
+  resolved "https://registry.yarnpkg.com/strict-uri-encode/-/strict-uri-encode-1.1.0.tgz#279b225df1d582b1f54e65addd4352e18faa0713"
 
 string-length@^2.0.0:
   version "2.0.0"