Support the latest EFS client

[dtan4]

WHAT

Upgrade EFS code to support the latest EFS client, and specify the dependency version to use aws-sdk-efs 1.13.0 or above.

WHY

Current code fails the test

Failures:

  1) Terraforming::Resource::EFSFileSystem.tf should generate tf
     Failure/Error: client.stub_responses(:describe_file_systems, file_systems: [efs_description_0, efs_description_1])

     ArgumentError:
       parameter validator found 2 errors:
         - missing required parameter params[:file_systems][0][:tags]
         - missing required parameter params[:file_systems][1][:tags]
     # ./spec/lib/terraforming/resource/efs_file_system_spec.rb:39:in `block (2 levels) in <module:Resource>'

  2) Terraforming::Resource::EFSFileSystem.tfstate should generate tfstate
     Failure/Error: client.stub_responses(:describe_file_systems, file_systems: [efs_description_0, efs_description_1])

     ArgumentError:
       parameter validator found 2 errors:
         - missing required parameter params[:file_systems][0][:tags]
         - missing required parameter params[:file_systems][1][:tags]
     # ./spec/lib/terraforming/resource/efs_file_system_spec.rb:39:in `block (2 levels) in <module:Resource>'

Finished in 2.71 seconds (files took 1.84 seconds to load)
226 examples, 2 failures

Failed examples:

rspec ./spec/lib/terraforming/resource/efs_file_system_spec.rb:43 # Terraforming::Resource::EFSFileSystem.tf should generate tf
rspec ./spec/lib/terraforming/resource/efs_file_system_spec.rb:66 # Terraforming::Resource::EFSFileSystem.tfstate should generate tfstate

[coveralls]

Coverage remained the same at 100.0% when pulling 07543bf on dtan4/support-latest-efs into 1ba96b9 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 07543bf on dtan4/support-latest-efs into 1ba96b9 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling d5f709f on dtan4/support-latest-efs into 1ba96b9 on master.

[dtan4]

Bundler 2.x doesn't support Ruby < 2.3.
This Ruby is no longer supported officially , so I'll also drop this Ruby's support with #452 macOS' system Ruby is still 2.3.7p456.

Bundler: Announcing Bundler 2.0

Removed support for Ruby < 2.3

Fetching gem metadata from https://rubygems.org/.........
Fetching gem metadata from https://rubygems.org/.
Resolving dependencies...
Bundler could not find compatible versions for gem "bundler":
  In Gemfile:
    bundler (~> 1.7)
  Current Bundler version:
    bundler (2.0.1)
This Gemfile requires a different version of Bundler.
Perhaps you need to update Bundler by running `gem install bundler`?
Could not find gem 'bundler (~> 1.7)' in any of the relevant sources:
  the local ruby installation