bump version to 0.7.0.pre2
bump version to 0.7.0.pre2

kshmir/azure-sdk-for-ruby,alexderz/azure-sdk-for-ruby,wastoresh/azure-sdk-for-ruby,Azure/azure-sdk-for-ruby,devigned/azure-sdk-for-ruby,theckman/azure-sdk-for-ruby,Azure/azure-sdk-for-ruby,oaastest/azure-sdk-for-ruby,devigned/azure-sdk-for-ruby