Update base64 requirement from ~> 0.2.0 to >= 0.2, < 0.4

Updates the requirements on [base64](https://github.com/ruby/base64) to permit the latest version.
- [Release notes](https://github.com/ruby/base64/releases)
- [Commits](ruby/base64@v0.2.0...v0.3.0)

---
updated-dependencies:
- dependency-name: base64
  dependency-version: 0.3.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

fog-aws.gemspec

@@ -28,7 +28,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'rubyzip', '~> 2.4.1'
   spec.add_development_dependency 'shindo',  '~> 0.3'
 
-  spec.add_dependency 'base64', '~> 0.2.0'
+  spec.add_dependency 'base64', '>= 0.2', '< 0.4'
   spec.add_dependency 'fog-core', '~> 2.6'
   spec.add_dependency 'fog-json', '~> 1.1'
   spec.add_dependency 'fog-xml', '~> 0.1'