Update parser gem to eliminate Ruby 2.7.5 warning

What does this MR do and why?

This eliminates the warning:

warning: parser/current is loading parser/ruby27, which recognizes
warning: 2.7.4-compliant syntax, but you are running 2.7.5.
warning: please see https://github.com/whitequark/parser#compatibility-with-ruby-mri.

Full diff: https://my.diffend.io/gems/parser/3.0.2.0/3.0.3.2

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