Add node v16 to ci matrix, and remove v10

[Anunayj]

Node v10 reached it's EOL on 30-Apr-2021, and therefore i don't
see a need for running ci on that, v16 would soon be the LTS
version (from 26-Oct-2021) therefore needs to be tested on.

[coveralls]

Pull Request Test Coverage Report for Build 1382817197

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.002%) to 62.248%

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Files with Coverage Reduction	New Missed Lines	%
lib/protocol/consensus.js	1	82.79%

Totals
Change from base Build 1368460091:	0.002%
Covered Lines:	21189
Relevant Lines:	31820

---

💛 - Coveralls

[pinheadmz]

Saving this output before adding more tests to the matrix on this branch:

@github-actions
Build / build (12.x) (pull_request) Successful in 3m
Details
@github-actions
Build / build (14.x) (pull_request) Successful in 4m
Details
@github-actions
Build / build (16.x) (pull_request) Successful in 3m
Details

[pinheadmz]

@Anunayj Ok I'm down for this, makes sense. We should also probably then bump the "minimum node version" wherever that is currently documented, like here: https://github.com/handshake-org/hsd#install

[Anunayj]

I think that is the only place that mentions the node version hsd-dev.org redirects to the readme too.