The plugin uses Semantic Versioning which in a nutshell means this:

Given a version number MAJOR.MINOR.PATCH, increment the:

1. MAJOR version when you make incompatible API changes,
2. MINOR version when you add functionality in a backwards-compatible manner, and
3. PATCH version when you make backwards-compatible bug fixes.

In other words: upgrading from v0.3 to v1.0 is not automatic and API has changed. But uprading from v1.0 to v1.1, v1.2 ... v1.9 will be easy without breaking changes.

So in your bower.json file you can use version ^2.0 which will allow upgrading to the latest version without breaking backwards compatibility:

"medium-editor-insert-plugin": "^2.0"