Upgrade "aws-xray-sdk-core" (#529)

```
% node --trace-warnings ./bin/node-lambda run
Running index.handler
==================================
event { key: 'value', key2: 'value2', other_key: 'other_value' }
==================================
Stopping index.handler
Success:
(node:10036) Warning: Accessing non-existent property 'padLevels' of module exports inside circular dependency
    at emitCircularRequireWarning (internal/modules/cjs/loader.js:814:11)
    at Object.get (internal/modules/cjs/loader.js:825:5)
    at Object.exports.setLevels (/pathto/node-lambda/node_modules/winston/lib/winston/common.js:35:14)
    at Object.<anonymous> (/pathto/node-lambda/node_modules/winston/lib/winston.js:83:8)
    at Module._compile (internal/modules/cjs/loader.js:1185:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1205:10)
    at Module.load (internal/modules/cjs/loader.js:1034:32)
    at Function.Module._load (internal/modules/cjs/loader.js:923:14)
    at Module.require (internal/modules/cjs/loader.js:1074:19)
    at require (internal/modules/cjs/helpers.js:72:18)
```

'winston' was the cause.
I upgraded 'aws-xray-sdk-core' because it was dependent on 'winston'.
(Relatedly, 'winston' is also getting an upgrade.)

Not directly related to the warning, but I've also upgraded packages other than 'aws-xray-sdk-core'.