Bugfix: missing leaflet dependency

[nickyadvokaat]

An error occurs when cloning the repo and running the commands:

• cd widgets
• mvn clean install -P yarn-start

Missing the leaflet package. Needed to run:

• yarn add leaflet -D in widgets directory

[vvlladd28]

This is a perfect workaround, but the fix is to add the leaflet dependency to thingsboard package. We updated yarn.lock file to the correct version.