Use es6/es2015 target for ESM output

es5 does not support class constructors and hence lead to issues.

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- `TypeError` issue related to constructors using js-waku in a JS project
+  ([#323](https://github.com/status-im/js-waku/issues/323)).
+
 ## [0.14.1] - 2021-10-22
 
 ### Fixed

package.json

@@ -19,7 +19,7 @@
     "build": "run-s build:**",
     "build:main": "tsc -p tsconfig.json",
     "build:dev": "tsc -p tsconfig.dev.json",
-    "build:esm": "tsc --module es2015 --target es5 --outDir build/esm",
+    "build:esm": "tsc --module es2015 --target es2015 --outDir build/esm",
     "build:umd": "webpack --config webpack.config.js",
     "build:umd:min": "webpack --config webpack.config.min.js",
     "build:umd:bundle": "webpack --config webpack.config.bundle.js",