Add Helmet to node server dependencies

[caz-gh]

Description

Added Helmet 4.6.0 (latest) to the list of node dependencies. The default config options are used, and more info on which response headers are set by default can be seen here.

Here are the response headers when using Helmet on a new Wasp app:

And here are the response headers without Helmet on a new Wasp app:

Fixes #22

Type of change

Please select the option(s) that is more relevant.

• Code cleanup
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update