fix(symlinked resources): configure the babelWD

[briandipalma]

By specifying the babelWD as being the process cwd we allow preset and
plugin resolution to occur relative to the directory where webpack is
running. This should resolve issues where presets and plugins could not
be resolved.

closes: #166, #179

[briandipalma]

This PR depends on a babel PR being merged babel/babel#3454

[loganfsmyth]

Babel 7.x now has a cwd option that defaults to process.cwd() and is used to resolve string-paths plugins/presets/paths passed to Babel via babel-loader's options. Given that, this should be resolved.