ci: Changes to CI configuration and support ruby 2.5 and 2.6

ci: Changes to CI configuration and support ruby 2.5 and 2.6

Author: Mikemosca

README.md

@@ -401,6 +401,8 @@ Tested on:
 * MRI Ruby (RVM): 2.5.1, 2.6.1
 * RubyInstaller (Windows x64): 2.5.1, 2.6.1
 
+2.3.7 and 2.4.4 should still work but support will be deprecated in next major release.
+
 ## Contributing
 
 See [CONTRIBUTING.md][CONTRIBUTING].

ibm_watson.gemspec

@@ -12,7 +12,7 @@ Gem::Specification.new do |spec|
   spec.summary = "Official client library to use the IBM Watson Services"
   spec.homepage = "https://www.github.com/watson-developer-cloud"
   spec.licenses = ["Apache-2.0"]
-  spec.required_ruby_version = ">= 2.5"
+  spec.required_ruby_version = ">= 2.3"
 
   # Prevent pushing this gem to RubyGems.org. To allow pushes either set the 'allowed_push_host'
   # to allow pushing to a single host or delete this section to allow pushing to any host.