Fix [_1,_2,_3] parameters (conflict with Ruby 2.7.0); Updated gems and ruby versions.

[jasnow]

• Fix [_1,_2,_3] parameters as they are numbered parameters in Ruby 2.7.0.
• Updated gems and ruby versions in .travis.yml file.
• Add 2.7.0 to .travis.yml file.
• Removed 2.1.0 from .travis.yml file.

[jasnow]

@halostatue - You are welcome to change my changes before releasing them if you wish. Happy Holidays....

[nehresma]

Bumped into this this morning. Was going to create a PR and saw @jasnow was already on top of it. Thank you!

[jasnow]

U R Welcome

[halostatue]

Thanks for your contribution!

mime-types 3.3 was released in September, so this will be version 3.3.1.

[jasnow]

Verified in release 3.3.1 of gem.