chore: Remove cp-file module (#1230)

This slightly reduces the amount of code nyc loads by using the core
fs.copyFile function.  Clarify `package.json#engines` to show that
node.js 8.9.0 (LTS) is the oldest supported release.

index.js

@@ -3,7 +3,6 @@
 /* global __coverage__ */
 
 const cachingTransform = require('caching-transform')
-const cpFile = require('cp-file')
 const findCacheDir = require('find-cache-dir')
 const fs = require('./lib/fs-promises')
 const os = require('os')
@@ -225,13 +224,23 @@ class NYC {
 
       const concurrency = output ? os.cpus().length : 1
       if (this.config.completeCopy && output) {
+        const files = await glob(path.resolve(input, '**'), {
+          dot: true,
+          nodir: true,
+          ignore: ['**/.git', '**/.git/**', path.join(output, '**')]
+        })
+        const destDirs = new Set(
+          files.map(src => path.dirname(path.join(output, path.relative(input, src))))
+        )
+
+        await pMap(
+          destDirs,
+          dir => mkdirp(dir),
+          { concurrency }
+        )
         await pMap(
-          await glob(path.resolve(input, '**'), {
-            dot: true,
-            nodir: true,
-            ignore: ['**/.git', '**/.git/**', path.join(output, '**')]
-          }),
-          src => cpFile(src, path.join(output, path.relative(input, src))),
+          files,
+          src => fs.copyFile(src, path.join(output, path.relative(input, src))),
           { concurrency }
         )
       }

package.json

@@ -59,7 +59,6 @@
     "@istanbuljs/schema": "^0.1.1",
     "caching-transform": "^4.0.0",
     "convert-source-map": "^1.7.0",
-    "cp-file": "^7.0.0",
     "decamelize": "^1.2.0",
     "find-cache-dir": "=3.0.0",
     "find-up": "^4.1.0",
@@ -96,7 +95,7 @@
     "which": "^2.0.1"
   },
   "engines": {
-    "node": ">=8"
+    "node": ">=8.9"
   },
   "homepage": "https://istanbul.js.org/",
   "repository": {

test/instrument.js

@@ -6,7 +6,6 @@ const { promisify } = require('util')
 
 const t = require('tap')
 const makeDir = require('make-dir')
-const cpFile = require('cp-file')
 const isWindows = require('is-windows')()
 const rimraf = promisify(require('rimraf'))
 
@@ -243,7 +242,7 @@ t.test('can write files in place with --in-place switch', async t => {
   const sourceDir = path.resolve(fixturesCLI, 'instrument-inplace')
   await makeDir(outputDir)
   await Promise.all(['package.json', 'file1.js', 'file2.js'].map(
-    file => cpFile(path.join(sourceDir, file), path.join(outputDir, file))
+    file => fs.copyFile(path.join(sourceDir, file), path.join(outputDir, file))
   ))
 
   const { status } = await runNYC({