fix: Resolve TypeScript errors

Signed-off-by: Hermes Agent <hermes@nosuchhost>

client/node_modules/level-concat-iterator/example.js

@@ -0,0 +1,13 @@
+var level = require('level')
+var concat = require('.')
+
+level('DB', function (err, db) {
+  if (err) throw err
+  db.put('foo', 'bar', function (err) {
+    if (err) throw err
+    concat(db.iterator(), function (err, data) {
+      if (err) throw err
+      console.log(data)
+    })
+  })
+})