Fix subscription-widget node engine version

[rafaelalmeidatk]

Checklist

• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them.
• I updated my branch with the master branch.

If you execute lerna bootstrap it will try to install subscription-widget and it will fail:

lerna ERR! yarn install --mutex network:42424 --non-interactive stderr:
warning Waiting for the other yarn instance to finish (5655)
warning Waiting for the other yarn instance to finish (5674)
error @sendgrid/[email protected]: The engine "node" is incompatible with this module. Expected version "4.1.1".
error Found incompatible module

This is due the node version being locked to a old version of node (4.1.1). This PR changes the node version to be compatible with all the other packages (>=6.0.0)

[thinkingserious]

Hello @rafaelalmeidatk,

Thanks again for the PR!

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[thinkingserious]

Hello @rafaelalmeidatk,

Thanks again for the PR!

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[thinkingserious]

Hello @rafaelalmeidatk,

Thanks again for the PR!

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