Remove extra empty line from README template

[r7kamura]

What was the end-user or developer problem that led to this PR?

bundle gem my_gem --mit generates README.md that contains extra empty line like this:

## Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/r7kamura/my_gem.


## License

The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).

What is your fix for the problem, implemented in this PR?

Removed an empty line placed before the License section from README template (README.md.tt).

Make sure he following tasks are checked

• Describe the problem / feature
• Write tests for features and bug fixes
• Write code to solve the problem
• Make sure you follow the current code style and write meaningful commit messages without tags

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[deivid-rodriguez]

Thanks!