Remove duplicate transform-regenerator dependency

[akofman]

It looks like babel-plugin-transform-regenerator is already a dependency of babel-preset-es2015 in a different version :

$npm ls babel-plugin-transform-regenerator 
[email protected] 
├── [email protected]
└─┬ [email protected]
  └─┬ [email protected]
    └── [email protected]

This can causes some trouble when using regeneratorRuntime but to ensure the older npm compatibility we have to keep this dependency.
So I just updated its version to the same version found from [email protected].

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