Remove Object.assign usage

[nylon22]

🐛 Bug report

Current Behavior

Object.assign is used at the following locations:

• sdk-js/packages/upload-core/src/upload.js

  Line 95 in c0ab8e9

  Object.assign(metadata, this.options.metadata);

• sdk-js/packages/env-var/src/index.js

  Line 58 in c0ab8e9

  Object.assign(environments, envs);

• sdk-js/packages/env-var/src/index.js

  Line 66 in c0ab8e9

  Object.assign(specificEnvironments, envs);

• https://github.com/Availity/sdk-js/blob/master/packages/exceptions-core/src/index.js#L123

Object.assign is not supported in IE:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign#Browser_compatibility

Expected behavior

Object.assign is not used

Suggested solution(s)

We either polyfill Object.assign or use the spread operator. or perhaps use the extend method from lodash. I'm partial to the spread operator.

[jordan-a-young]

I vote for using the spread operator too. Looks like it should cover the cases listed.