Replaced fs.promises.readFile() with fs.readFile(), since `fs.pro…

…mises` does not exist in Node 8

src/cache.ts

@@ -1,6 +1,6 @@
-import * as fs from "fs";
 import * as SVGO from "svgo";
 import { GroupedImageNodes, ImageNodeGroup } from "./image-node";
+import { readFile } from "./read-file";
 
 /**
  * A cache of the contents of of SVG files. This saves us from reading the same files
@@ -56,7 +56,7 @@ export class SvgCache extends Map<string, string> {
     this._hits += (nodes.length - 1);
 
     // Read the SVG file
-    let content = await fs.promises.readFile(path, "utf8");
+    let content = await readFile(path, "utf8");
 
     // Optimize the contents, if enabled
     if (optimizer) {

src/read-file.ts

@@ -0,0 +1,11 @@
+import * as fs from "fs";
+
+/**
+ * Asynchronously reads the specified file and returns its contents as a string.
+ */
+export async function readFile(path: string, encoding: string): Promise<string> {
+  return new Promise((resolve, reject) => {
+    // tslint:disable-next-line: ban
+    fs.readFile(path, encoding, (err, contents) => err ? reject(err) : resolve(contents));
+  });
+}

test/utils/compare-contents.js

@@ -1,6 +1,6 @@
 "use strict";
 
-const fs = require("fs");
+const { readFile } = require("../../lib/read-file");
 const { expect } = require("chai");
 
 module.exports = compareContents;
@@ -9,6 +9,6 @@ module.exports = compareContents;
  * Compares the given file contents to the expected contents.
  */
 async function compareContents (actualContents, fileName) {
-  let expectedContents = await fs.promises.readFile(`test/fixtures/modified/${fileName}`, "utf8");
+  let expectedContents = await readFile(`test/fixtures/modified/${fileName}`, "utf8");
   expect(actualContents).to.equal(expectedContents);
 }