Malformed AMI name

[sixhobbits]

Currently the AMI name is based on the EC2 instance tag name. But the name of the instance allows more characters than the name of the AMI. For the instance I was trying to back up, the script throws this error:

2017-07-06T03:10:32.880Z	aa144caa-61f8-11e7-b3c3-515643d3a81c	{ [InvalidAMIName.Malformed: AMI names must be between 3 and 128 characters long, and may contain letters, numbers, '(', ')', '.', '-', '/' and '_']
message: 'AMI names must be between 3 and 128 characters long, and may contain letters, numbers, \'(\', \')\', \'.\', \'-\', \'/\' and \'_\'',
code: 'InvalidAMIName.Malformed',
time: Thu Jul 06 2017 03:10:32 GMT+0000 (UTC),
requestId: 'd0dc4e92-fe6c-4d3e-84ea-1e9bda700bc7',
statusCode: 400,
retryable: false,
retryDelay: 99.96723912190646 } 'InvalidAMIName.Malformed: AMI names must be between 3 and 128 characters long, and may contain letters, numbers, \'(\', \')\', \'.\', \'-\', \'/\' and \'_\'\n at Request.extractError (/var/runtime/node_modules/aws-sdk/lib/services/ec2.js:50:35)\n at Request.callListeners (/var/runtime/node_modules/aws-sdk/lib/sequential_executor.js:105:20)\n at Request.emit (/var/runtime/node_modules/aws-sdk/lib/sequential_executor.js:77:10)\n at Request.emit (/var/runtime/node_modules/aws-sdk/lib/request.js:678:14)\n at Request.transition (/var/runtime/node_modules/aws-sdk/lib/request.js:22:10)\n at AcceptorStateMachine.runTo (/var/runtime/node_modules/aws-sdk/lib/state_machine.js:14:12)\n at /var/runtime/node_modules/aws-sdk/lib/state_machine.js:26:10\n at Request.<anonymous> (/var/runtime/node_modules/aws-sdk/lib/request.js:38:9)\n at Request.<anonymous> (/var/runtime/node_modules/aws-sdk/lib/request.js:680:12)\n at Request.callListeners (/var/runtime/node_modules/aws-sdk/lib/sequential_executor.js:115:18)'

I'll try submit a pull request to fix this in a bit.