Fix docker bundler version

[evelynhasama]

Description

When running the Docker commands to set up one's local development environment, new developers were running into an error indicating bundler requires Ruby version >= __. To fix this, we specify the bundler version in the Dockerfile, as suggested in the discussion here: rubygems/bundler#6865

Test

• tested running docker commands locally on multiple computers

[saatvikkher]

ERROR:  Error installing rubygems-update:
        There are no versions of rubygems-update (= 3.5.5) compatible with your Ruby & RubyGems
        rubygems-update requires Ruby version >= 3.0.0. The current ruby version is 2.6.3.62.
ERROR:  While executing gem ... (NoMethodError)
    undefined method `version' for nil:NilClass

Maybe we should upgrade ruby version?