Bump version to 4.4.1

[josephfrazier]

Changes include:

• Remove no longer relevant lastIndex code from replace method, fixes https://github.com/slevithan/xregexp/issues/287
• Add browser field to package.json to fix webpack: https://github.com/slevithan/xregexp/pull/308

To generate this commit, I adapted the steps at https://github.com/slevithan/xregexp/pull/205#issuecomment-354236652

Here's a fuller list of changes that can be needed with new releases:

• Version number
  • Update version number and year in headers, config files, README.
  • Update year in LICENSE.
  • Update version number in XRegExp.version.
• Publish
  • Publish new git tag. E.g.:
  • git tag -a v3.1.0 -m "Release 3.1.0".
  • git push origin v3.1.0.
  • npm publish.

[josephfrazier]

Hmm, seems like the build hasn't started yet:

I assume this is because the PR is from a fork, and we haven't yet changed a setting to allow forks to run the github actions: https://github.blog/2020-08-03-github-actions-improvements-for-fork-and-pull-request-workflows/

But, it might make more sense for me to just open a PR from a branch in this repo, rather than my fork

[josephfrazier]

closing in favor of https://github.com/slevithan/xregexp/pull/312