Update bundler requirement from ~> 1.16 to ~> 2.3 in /docs

[dependabot[bot]]

Updates the requirements on bundler to permit the latest version.

Release notes

Sourced from bundler's releases.

bundler-v2.3.4

Enhancements:

• Improve error message when BUNDLED WITH version does not exist #5205

Bug fixes:

• Fix bundle update --bundler no longer updating lockfile #5224

Changelog

Sourced from bundler's changelog.

2.3.4 (December 29, 2021)

Enhancements:

• Improve error message when BUNDLED WITH version does not exist #5205

Bug fixes:

• Fix bundle update --bundler no longer updating lockfile #5224

2.3.3 (December 24, 2021)

Bug fixes:

• Fix locked bundler not installed to the right path when deployment is set #5217

2.3.2 (December 23, 2021)

Enhancements:

• Remove unnecessary lockfile upgrade warning #5209

2.3.1 (December 22, 2021)

Enhancements:

• Vendor latest thor with fixes for latest did_you_mean deprecations #5202
• Avoid unnecessary shellwords require on newer rubygems #5195
• Re-exec prepending command with Gem.ruby if $PROGRAM_NAME is not executable #5193

2.3.0 (December 21, 2021)

Features:

• Change bundle install with a lockfile to respect the BUNDLED WITH bundler version #4076

Enhancements:

• Print warning when running Bundler on potentially problematic RubyGems & Ruby combinations #5177
• Error tracing should be printed to stderr #5179
• Add github and ref options to bundle add #5159
• Add require parameter to bundle add #5021
• Enable parallel installation on Windows by default #4822
• More logging when compact index is not used and we fallback to other APIs #4546
• bundle gem generated MiniTest file and class now start with 'test' #3893
• Add Bundler::Definition.no_lock accessor for skipping lock file creation/update #3401

Bug fixes:

• Fix crash when when no platform specific matches exist and show a proper error #5168

... (truncated)

Commits

• 2296a0d Merge pull request #5238 from rubygems/release/bundler_2.3.4_rubygems_3.3.4
• 5b5f547 Bump Rubygems version to 3.3.4
• 9cd1b7b Changelog for Rubygems version 3.3.4
• 1713e06 Bump Bundler version to 2.3.4
• 0ea2aba Changelog for Bundler version 2.3.4
• fc431af Merge pull request #5224 from rubygems/bundle-update-bundler-no-longer-updates
• 4ef4063 Merge pull request #5191 from rubygems/fix_gem_update_system_when_latest_vers...
• 8ac88bb Merge pull request #5230 from rubygems/dont_redownload_rubygems_update
• 097d4e9 Merge pull request #5205 from rubygems/use_bundler_installer_to_install_the_b...
• 8e4d6fc Merge pull request #5226 from rubygems/fix_ruby_head_ci
• Additional commits viewable in compare view

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[DamonU2]

@jvanulde All three are working fine for me, can be merged