Jest errors out when importing this package #14

Our app was hitting the following error when we added tests that relied on a package that relied on this package:

TypeError: Cannot assign to read only property 'name' of function 'function SequenceMatcher(isjunk, a, b, autojunk) {

      at ../../node_modules/difflib/lib/difflib.js:78:25
      at call (../../node_modules/difflib/lib/difflib.js:660:3)
      at Object.<anonymous> (../../node_modules/difflib/lib/difflib.js:1486:4)
      at Object.<anonymous> (../../node_modules/difflib/index.js:1:18)

with the issue being these two lines:

• difflib.js/lib/difflib.js

  Line 78 in e11553b

  SequenceMatcher.name = 'SequenceMatcher';

• difflib.js/lib/difflib.js

  Line 740 in e11553b

  Differ.name = 'Differ';

Per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/name, the issue is that the name property for a function is not writable, and so doing assignment isn't allowed, and will do nothing in non-strict contexts, or error in strict contexts. For an example of the former context, see this REPL output:

> a = (function() { console.log('foo') });
[Function: a]
> a.name
'a'
> a.name = 'b'
'b'
> a.name
'a'

If assigning the name is necessary, it needs to be done by doing Object.defineProperty instead, which can bypass the writable attribute:

> a = (function() { console.log('foo') });
[Function: a]
> a.name
'a'
> Object.defineProperty(a, 'name', { value: 'b' })
[Function: b]
> a
[Function: b]
> a.name
'b'

To workaround this, for now we're mocking out the dependency with a stub as we don't depend on the output, but it'd be nice to not have to.