Updated Ruby version requirement.
Updated Ruby version requirement.

ADAL Ruby uses Array#h, which was apparently not added until 2.1.0.

AzureAD/azure-activedirectory-library-for-ruby,AzureAD/azure-activedirectory-library-for-ruby,cosmincojocar/azure-activedirectory-library-for-ruby,cosmincojocar/azure-activedirectory-library-for-ruby