Bug with the newer version of aws-ruby-sdk (>= 2.6.24)

[riywo]

Since this plugin uses private API (Aws::CredentialProviderChain), breaking changes sometimes happen...

Error: test_record_count(KinesisStreamsOutputTest):
  NoMethodError: undefined method `instance_profile_credentials_retries' for #<#<Class:0x007fc9c26dce30>:0x007fc9c616be48>
  Did you mean?  instance_variable_defined?
/Users/iwanagar/.anyenv/envs/rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/aws-sdk-core-2.6.24/lib/aws-sdk-core/credential_provider_chain.rb:27:in `providers'
/Users/iwanagar/.anyenv/envs/rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/aws-sdk-core-2.6.24/lib/aws-sdk-core/credential_provider_chain.rb:11:in `resolve'
/Users/iwanagar/github/aws-fluent-plugin-kinesis/lib/fluent/plugin/kinesis_helper/credentials.rb:43:in `default_credentials_provider'
/Users/iwanagar/github/aws-fluent-plugin-kinesis/lib/fluent/plugin/kinesis_helper/credentials.rb:34:in `credentials'
/Users/iwanagar/github/aws-fluent-plugin-kinesis/lib/fluent/plugin/kinesis_helper/api.rb:42:in `client_options'
/Users/iwanagar/github/aws-fluent-plugin-kinesis/lib/fluent/plugin/kinesis_helper/client.rb:19:in `client'
/Users/iwanagar/github/aws-fluent-plugin-kinesis/lib/fluent/plugin/kinesis_helper/api.rb:28:in `configure'
/Users/iwanagar/.anyenv/envs/rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/fluentd-0.14.9/lib/fluent/test/base.rb:60:in `configure'
/Users/iwanagar/github/aws-fluent-plugin-kinesis/test/plugin/test_out_kinesis_streams.rb:47:in `create_driver'
/Users/iwanagar/github/aws-fluent-plugin-kinesis/test/plugin/test_out_kinesis_streams.rb:123:in `test_record_count'