removed Java 7 as an option on README.

update pom.xml in swagger components to 2.3.1

update version to 2.3.0

Merge pull request swagger-api#6071 from swagger-api/update-parser

updated parser

Merge pull request swagger-api#4889 from swagger-api/release-prepare

update to release versions

Merge pull request swagger-api#3549 from swagger-api/release-prepare

updated versions for release

Merge pull request swagger-api#3388 from swagger-api/release-prepare

updated versions for release

Merge pull request swagger-api#2515 from swagger-api/release-prepare

release prepare

fixed javadoc plugin