chore: Switch from nyc to c8 for code coverage

nyc was no longer working with the ES module imports, and
c8 is in any case more efficient, using native V8 coverage
made available in Node.js 10.12.0 and later.

common.mk

@@ -9,7 +9,6 @@ DOC_DESTINATION := $(subst @fluent, ../html, $(PACKAGE))
 export SHELL := /bin/bash
 ESLINT ?= $(ROOT)node_modules/.bin/eslint
 TSC ?= $(ROOT)node_modules/.bin/tsc
-NYC ?= $(ROOT)node_modules/.bin/nyc
 MOCHA ?= $(ROOT)node_modules/.bin/mocha
 ROLLUP ?= $(ROOT)node_modules/.bin/rollup
 TYPEDOC ?= $(ROOT)node_modules/.bin/typedoc
@@ -29,7 +28,7 @@ TYPEDOC_CMD = $(TYPEDOC) src/index.?s \
 	--includeVersion \
 	$(NULL)
 
-MOCHA_CMD =@$(NYC) --reporter=text --reporter=html $(MOCHA) \
+MOCHA_CMD = npx c8 $(MOCHA) \
 	--recursive --ui tdd \
 	$(MOCHA_EXTRA_ARGS) \
 	test/**/*_test.js \

fluent-dom/package.json

@@ -34,7 +34,7 @@
     "format"
   ],
   "scripts": {
-    "test": "mocha -ui tdd --require ./test/index.js 'test/*_test.js'"
+    "test": "c8 mocha -ui tdd --require ./test/index.js 'test/*_test.js'"
   },
   "engines": {
     "node": ">=12.0.0",