add base64 as explicit dependency (#3186)

Author: HoneyryderChuck

gems/aws-sdk-core/aws-sdk-core.gemspec

@@ -1,9 +1,8 @@
 # frozen_string_literal: true
 
 Gem::Specification.new do |spec|
-
   spec.name          = 'aws-sdk-core'
-  spec.version       = File.read(File.expand_path('../VERSION', __FILE__)).strip
+  spec.version       = File.read(File.expand_path('VERSION', __dir__)).strip
   spec.summary       = 'AWS SDK for Ruby - Core'
   spec.description   = 'Provides API clients for AWS. This gem is part of the official AWS SDK for Ruby.'
   spec.author        = 'Amazon Web Services'
@@ -12,14 +11,16 @@ Gem::Specification.new do |spec|
   spec.require_paths = ['lib']
   spec.files         = Dir['LICENSE.txt', 'CHANGELOG.md', 'VERSION', 'lib/**/*.rb', 'sig/**/*.rbs', 'ca-bundle.crt']
 
-  spec.add_dependency('jmespath', '~> 1', '>= 1.6.1') # necessary for secure jmespath JSON parsing
+  spec.add_dependency('aws-eventstream', '~> 1', '>= 1.3.0') # necessary for binary eventstream
   spec.add_dependency('aws-partitions', '~> 1', '>= 1.992.0') # necessary for new endpoint resolution
   spec.add_dependency('aws-sigv4', '~> 1.9') # necessary for s3 express auth/native sigv4a support
-  spec.add_dependency('aws-eventstream', '~> 1', '>= 1.3.0') # necessary for binary eventstream
+
+  spec.add_dependency('base64')
+  spec.add_dependency('jmespath', '~> 1', '>= 1.6.1') # necessary for secure jmespath JSON parsing
 
   spec.metadata = {
     'source_code_uri' => 'https://github.com/aws/aws-sdk-ruby/tree/version-3/gems/aws-sdk-core',
-    'changelog_uri'   => 'https://github.com/aws/aws-sdk-ruby/tree/version-3/gems/aws-sdk-core/CHANGELOG.md'
+    'changelog_uri' => 'https://github.com/aws/aws-sdk-ruby/tree/version-3/gems/aws-sdk-core/CHANGELOG.md'
   }
 
   spec.required_ruby_version = '>= 2.5'