Added checks to make sure the specified track exists

Added precondition checks to validate input files and paths to return more informative error messages as per #2

node_modules/@babel/plugin-syntax-object-rest-spread/README.md

@@ -0,0 +1,19 @@
+# @babel/plugin-syntax-object-rest-spread
+
+> Allow parsing of object rest/spread
+
+See our website [@babel/plugin-syntax-object-rest-spread](https://babeljs.io/docs/en/next/babel-plugin-syntax-object-rest-spread.html) for more information.
+
+## Install
+
+Using npm:
+
+```sh
+npm install --save-dev @babel/plugin-syntax-object-rest-spread
+```
+
+or using yarn:
+
+```sh
+yarn add @babel/plugin-syntax-object-rest-spread --dev
+```