Upgraded dependencies and migrated to flutter Lints and flutter tests.

[prakasharyaman]

Changes

1. Converted StringSimilarity to mixin for better code reusability.
2. Changes test package to flutter_test for improved management.
3. Use of flutter_lints insted of pedantic (which is discontinued).
4. Version upgrade from 2.0.0 to 2.0.1 .
5. Addition of testing it on web using Dart pad

Overall:

Credit: @jeremylandon for creating this package.