Update README screenshot.
Update README screenshot.

rasata/MailDev,xavierpriour/MailDev,sendwithus/tool-maildev,AlexDpy/MailDev,xavierpriour/MailDev,rasata/MailDev,AlexDpy/MailDev,strategicdata/MailDev,sendwithus/tool-maildev,strategicdata/MailDev,strategicdata/MailDev