Merge pull request #903 from hzh2005525/master

xxl-job-admin/src/main/resources/application.properties

 spring.mail.properties.mail.smtp.auth=true
 spring.mail.properties.mail.smtp.starttls.enable=true
 spring.mail.properties.mail.smtp.starttls.required=true
+spring.mail.properties.mail.smtp.socketFactory.class=javax.net.ssl.SSLSocketFactory
 
 ### xxl-job, access token
 xxl.job.accessToken=