Remove node 14 ci (require node >= 18)

[aljones15]

Removes node 14 from the CI tests and sets node 18 as the lowest test and engine version.

p.s. node 14 is throwing this error when running the test suite:

file:///home/runner/work/vc/vc/node_modules/@digitalbazaar/ecdsa-multikey/lib/crypto.js:4
import {webcrypto} from 'node:crypto';
^^^^^^^^^
SyntaxError: The requested module 'node:crypto' does not provide an export named 'webcrypto'
at ModuleJob._instantiate (internal/modules/esm/module_job.js:124:21)
at async ModuleJob.run (internal/modules/esm/module_job.js:179:5)
at async Loader.import (internal/modules/esm/loader.js:178:24)
at async formattedImport (/home/runner/work/vc/vc/node_modules/mocha/lib/nodejs/esm-utils.js:9:14)
at async Object.exports.requireOrImport (/home/runner/work/vc/vc/node_modules/mocha/lib/nodejs/esm-utils.js:42:28)
at async Object.exports.loadFilesAsync (/home/runner/work/vc/vc/node_modules/mocha/lib/nodejs/esm-utils.js:100:20)
at async singleRun (/home/runner/work/vc/vc/node_modules/mocha/lib/cli/run-helpers.js:125:3)
at async Object.exports.handler (/home/runner/work/vc/vc/node_modules/mocha/lib/cli/run.js:370:5)

could be a duplicate of:
https://github.com/digitalbazaar/vc/pull/156/files

please note this could be a patch release as node 14 support is broken.

I am submitting this as a patch release as the current release is broken in node 14 and node 16 throws warnings on install and might have broken functionality not in the test suite.

[codecov-commenter]

Codecov Report

Merging #160 (b4cc555) into main (d491d91) will decrease coverage by 0.22%.
Report is 22 commits behind head on main.
The diff coverage is 78.72%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #160      +/-   ##
==========================================
- Coverage   87.27%   87.05%   -0.22%     
==========================================
  Files           4        4              
  Lines         770      811      +41     
==========================================
+ Hits          672      706      +34     
- Misses         98      105       +7     

Files	Coverage Δ
lib/index.js	87.19% <78.72%> (-0.27%)	⬇️

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[aljones15]

closing as multiple PRs address this issue.