Update parser gem to remove warning about wrong ruby version

What does this MR do?

Fix this warning when you execute any ruby/rails code in gitlab's project:

warning: parser/current is loading parser/ruby23, which recognizes
warning: 2.3.3-compliant syntax, but you are running 2.3.5.
warning: please see https://github.com/whitequark/parser#compatibility-with-ruby-mri.

Are there points in the code the reviewer needs to double check?

No, but here is how to test:

Before applying this, run rake -T you should see the warning above, do the same after, and it's gone.

Why was this MR needed?

The warning is annoying :)

We may also consider backporting this to 10.2.