[fix] handle-callback-err (closes #146)

[jmlopez-rod]

The current code for the rule as it stands has a bug. The line

const highlights = this.languageService.getDocumentHighlights(fileName, parameter.pos, [fileName]);

should be

const highlights = this.languageService.getDocumentHighlights(fileName, parameter.name.getStart(), [fileName]);

Making that change fixes issue #146. In this PR however, I have removed the usage of the languageService. Each call togetDocumentHighlights triggers a function which will search for the parameter in the document tree. The change I made is based on the prefer-arrow-function rule which keeps track of each function scope to determine if we make use of the error parameter. Based on some simple comparisons as noted on the issue we do get some performance with this change.

[blakeembrey]

Looks great! Does this handle the error parameter where it may be handled in a nested function? E.g.

function query (cb) {
  doThing(function (err) {
    closeConnection(function (closeErr) {
      cb(err || closeErr)
    })
  })
})

[jmlopez-rod]

@blakeembrey Yup. Seems like a good test to add to the custom regex examples.