chore: switch code coverage from Istanbul to Nyc

Istanbul is no longer maintained

.gitignore

@@ -1,5 +1,6 @@
 node_modules
 coverage
+.nyc_output
 test-snapshot/output-actual
 test-snapshot/output-expected/public
 test-snapshot/output-expected/metadata.json

.nycrc.yml

@@ -0,0 +1,7 @@
+all: true
+include:
+  - src/**
+  - bin/**
+reporter:
+  - html
+  - text-summary

package.json

@@ -28,7 +28,7 @@
   ],
   "scripts": {
     "lint": "standard && require-lint",
-    "unit": "istanbul cover node_modules/mocha/bin/_mocha",
+    "unit": "nyc npx mocha",
     "test": "npm run lint && npm run unit"
   },
   "dependencies": {
@@ -67,12 +67,11 @@
     "glob": "^7.1.6",
     "gm": "^1.23.1",
     "injectmd": "^1.0.0",
-    "istanbul": "^0.4.5",
     "markdown-toc": "^1.1.0",
     "mocha": "^8.2.1",
     "mock-fs": "^4.13.0",
     "mock-spawn": "^0.2.6",
-    "require-all": "^3.0.0",
+    "nyc": "^15.1.0",
     "require-lint": "^2.0.2",
     "should": "^13.2.3",
     "sinon": "^9.2.2",

test/helpers.js

@@ -1,11 +1,5 @@
-const path = require('path')
-const requireAll = require('require-all')
 const tmp = require('tmp')
 
-// require all source code
-// so that the coverage report is accurate
-requireAll(path.join(__dirname, '..', 'src'))
-
 // capture all unhandled rejected promises
 // and ensure the current test fails
 process.on('unhandledRejection', err => {