Drop support for Node 10

[jasonkuhrt]

What

• We support Node 10 today
• Drop it

Why

• Node 14 is out now, soon enters LTS
• Dropping Node 10 gives us worker support without needing code for fallback to spawn

How

• Maybe when Node 14 hits LTS is a good time to drop Node 10
• Maybe we should define a policy
• E.g. We only commit to supporting last two Node LTS versions

Notes

• What type of issue is this? Considering a refactor type for now...