Adds support for React 15.0.0

[EvHaus]

This PR adds support for React 15.

Changes made:

• Updated package.json's peerDependencies
• Updated package.json's devDependencies
• Updated tests to use react-dom/server for renderToStaticMarkup instead of react.
• The main Resolver.js code seems to already be using react-dom/server so no changes needed to be made there

Testing:

• All tests pass via npm run test
• Unable to run linting via npm run lint because the peerDependencies of eslint-config-future are not installed (resulting in eslint-config-future@2.1.1 requires a peer of babel-eslint@3.x but none was installed errors, etc..). And I was unable to manually install the required dependencies because eslint-config-future wants babel-eslint@3.1.x but that version of babel-eslint is broken due to this bug: https://github.com/babel/babel-eslint/issues/243 No idea of linting will pass as a result of this.

[pwmckenna]

@EvNaverniouk We'll probably need to make some updates to https://github.com/ericclemmons/eslint-config-future to get this to lint, or switch to something like eslint-config-airbnb (my personal preference is of course eslint-config-pwmckenna ;) ) Anyhow, I ran this branch against a different lint config that just checks for syntactic errors and every thing looked good, so this feels ready to merge and release.

@ericclemmons this will result in "" rather than <noscript/> for unresolved components, which is sort of a breaking change, however its the default behavior of the react peer dependency, so how do you feel about a patch release?

[pwmckenna]

@EvNaverniouk just published as 3.0.1. thanks for the PR!