update to webpack 4, update dependencies, update node, fix some eslint warnings

[glebtv]

This change is 

[justin808]

@glebtv Thank you! LGTM.

Before I merge:

1. @glebtv can you tell me how you verified this fix works for supported versions of Webpack?
2. Update https://github.com/shakacode/sass-resources-loader/blob/master/CHANGELOG.md. Is this a patch, minor, etc.?
3. Fix CI

@alexfedoseev Any comments?

+(review needed)
+(waiting on submitter)

Reviewed 16 of 16 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @glebtv)

---

src/utils/rewriteImports.js, line 15 at r1 (raw file):

};

export default function (error, file, contents, moduleContext, callback) {

@glebtv Why is this changing?

[justin808]

@glebtv can your updates include these or else close these as not relevant?

Bump diff from 3.3.1 to 3.5.0  dependencies
#94 opened 4 days ago by dependabot bot 
Bump is-my-json-valid from 2.16.1 to 2.20.0  dependencies
#93 opened 5 days ago by dependabot bot 
Bump handlebars from 4.0.10 to 4.1.2  dependencies
#92 opened 12 days ago by dependabot bot 
Bump sshpk from 1.13.1 to 1.16.1  dependencies
#90 opened 14 days ago by dependabot bot 

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @glebtv)

[justin808]

https://github.com/shakacode/sass-resources-loader/pulls

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @glebtv)

[glebtv]

1. I updated all of the dependencies. yarn outdated is empty both in package and in example.
2. Only tested on webpack 4 and node 12, tested on example from this repo and one medium-sized app.
3. Updated eslint configs, all of the code style changes are from updated eslint configs
4. Added a css-format test file, because in a real app I had a problem with CSS files (adding import directives to CSS file causes SASS to break for me with strange errors) - but was unable to reproduce in an example, solved for me by excluding *.css from this loader in my app.
5. CI fail is due to eslint errors on current code and new versions of eslint configs, I am not really sure how to fix them (if you want, I can add eslint-ignore on them)

[justin808]

Sounds good on the above! @glebtv

For the consistent-return, I think it's best to fix the code so it passes this. That means adding a few return undefined;

/home/travis/build/shakacode/sass-resources-loader/src/loader.js
  13:16  error  Expected to return a value at the end of function  consistent-return
  20:3   error  Unexpected dangling '_' in '__DEBUG__'             no-underscore-dangle
  75:2   error  Unnecessary semicolon                              no-extra-semi

Last one is easy.
2nd one maybe can be ignored.

/home/travis/build/shakacode/sass-resources-loader/src/utils/flattenArray.js
  1:36  error  Use the spread operator instead of '.apply()'  prefer-spread

https://eslint.org/docs/rules/prefer-spread

export default multidimensional => [].concat(...multidimensional);

/home/travis/build/shakacode/sass-resources-loader/src/utils/rewriteImports.js
15:16 error Expected to return a value at the end of function consistent-return
/home/travis/build/shakacode/sass-resources-loader/test/index.test.js
60:22 error Unexpected require() global-require
69:22 error Unexpected require() global-require
78:22 error Unexpected require() global-require
128:32 error Unexpected require() global-require

I think these should be ignored in the file.

[Judahmeek]

@justin808 do you want me to complete this PR?

[glebtv]

@justin808 Thank you for the feedback, I have fixed all the remaining ESLint problems.

[justin808]

-(review needed)
-(waiting on submitter)

Reviewed 5 of 5 files at r2.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @glebtv)

[justin808]

@glebtv @Judahmeek Can the rest of these be closed: https://github.com/shakacode/sass-resources-loader/pulls ?