Allow any version of webpack as a peerDependency

[lencioni]

Webpack 4 alpha has been released. In preparation for v4,
it seems reasonable to change this to allow *. This should cut
down on maintenance and avoid unnecessarily blocking folks
from updating going forward.

Please Read the CONTRIBUTING Guidelines
In particular the portion on Commit Message Formatting

Please check if the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe: peerDependency change

What is the current behavior? (You can also link to an open issue here)
Cannot be used with Webpack 4 alpha

What is the new behavior?
Can be used with Webpack 4 alpha

Does this PR introduce a breaking change?

• Yes
• No

If this PR contains a breaking change, please describe the following...

• Impact:
• Migration path for existing applications:
• Github Issue(s) this is regarding:

Other information:
It would be nice to put out a release of babel-loader that allows any version of webpack and also works with Babel 6.

[danez]

Can you please change this to >= 2 that is what it should be right now, as 1.x is not supported and will not work.

[danez]

Thank you very much.

[loganfsmyth]

Is using a range like this a good idea? Using * is bad practice and I feel like >=2 isn't better, future Webpack versions could still easily break things if they wanted. How about >=2 < 5?

[Andarist]

I second what @loganfsmyth said, it seems pretty much as * in disguise. Even specifying <5 is a little bit stretch as we do not have certainty that it will work for webpack@4 - it is not released after all.