Update dev dependency "prettier"

[mikeharder]

Overview

I tried updating to prettier@^2.0.5, but when I execute npm run format, there are a ton of formatting changes. Examples include:

• Spaces are added after the word "function" in function expressions
  • https://prettier.io/blog/2020/03/21/2.0.0.html#always-add-a-space-after-the-function-keyword-3903httpsgithubcomprettierprettierpull3903-by-j-f1httpsgithubcomj-f1-josephfrazierhttpsgithubcomjosephfrazier-sosukesuzukihttpsgithubcomsosukesuzuki-thorn0httpsgithubcomthorn0-7516httpsgithubcomprettierprettierpull7516-by-bakkothttpsgithubcombakkot
• Different indentation of multi-line expressions

In order to upgrade, I think we will need to either modify our config to make prettier@2 work more closely to prettier@1, or we will need to reformat nearly all our source files.

Breaking Changes

https://prettier.io/blog/2020/03/21/2.0.0.html#breaking-changes

Relevant breaking changes:

• Drop support for Node versions older than 10
  • Probably OK since we only build on Node 10 and above. Node 8 is only used for testing.
• Change default value for trailingComma to es5
  • Might be relevant since value is not set in https://github.com/Azure/azure-sdk-for-js/blob/master/sdk/.prettierrc.json, but we can always set a different value if we don't like the new default.
• Change default value for arrowParens to always
  • Already set to this value in our config
• Change default value for endOfLine to lf
  • Already set to this value in our config