fix: remove the unmaintained mkdirp dependency

using fs.promises feature detection

bin/c8.js

@@ -3,7 +3,7 @@
 
 const foreground = require('foreground-child')
 const { outputReport } = require('../lib/commands/report')
-const mkdirp = require('mkdirp')
+const { promises } = require('fs')
 const { promisify } = require('util')
 const rimraf = require('rimraf')
 const {
@@ -25,7 +25,9 @@ async function run () {
       await promisify(rimraf)(argv.tempDirectory)
     }
     // allow c8 to run on Node 8 (coverage just won't work).
-    await promisify(mkdirp)(argv.tempDirectory)
+    if (promises) {
+      await promises.mkdir(argv.tempDirectory, { recursive: true })
+    }
 
     process.env.NODE_V8_COVERAGE = argv.tempDirectory
     foreground(hideInstrumenterArgs(argv), async (done) => {

package.json

@@ -39,7 +39,6 @@
     "istanbul-lib-coverage": "^2.0.1",
     "istanbul-lib-report": "^2.0.1",
     "istanbul-reports": "^2.0.0",
-    "mkdirp": "^0.5.1",
     "rimraf": "^2.6.2",
     "test-exclude": "^5.0.0",
     "v8-to-istanbul": "^3.1.1",

test/fixtures/disable-fs-promises.js

@@ -0,0 +1,4 @@
+const fs = require('fs');
+
+Object.defineProperty(fs, 'promises', {value: undefined});
+require('../../bin/c8.js');

test/legacy-node.js

@@ -0,0 +1,20 @@
+/* global describe, it */
+
+const { execFile } = require('child_process')
+const { mkdir } = require('fs').promises
+const { join } = require('path')
+const { promisify } = require('util')
+const c8Path = require.resolve('./fixtures/disable-fs-promises')
+const nodePath = process.execPath
+
+describe('c8 on Node.js < 10', () => {
+  it('doesn\'t crash', async () => {
+    await mkdir(join(__dirname, '..', 'tmp', 'legacy-nodejs'))
+    await promisify(execFile)(nodePath, [
+      c8Path,
+      '--temp-directory=tmp/legacy-nodejs',
+      'node',
+      '--version'
+    ])
+  })
+})