Use async fs on new linecounter tests (#1446)

test/lineCounter.js

@@ -1,8 +1,8 @@
-const fs = require('fs');
+const fs = require('../src/utils/fs');
 const assert = require('assert');
 const lineCounter = require('../src/utils/lineCounter');
 
-describe('line counter', () => {
+describe('line counter', async function() {
   it('counts number of lines of a string', () => {
     const input = ` line 1
       line 2
@@ -11,8 +11,8 @@ describe('line counter', () => {
     assert(lineCounter(input) === 3);
   });
 
-  it('counts number of lines of a file from disk', () => {
-    const input = fs.readFileSync('./test/lineCounter.js').toString();
+  it('counts number of lines of a file from disk', async function() {
+    const input = (await fs.readFile('./test/lineCounter.js')).toString();
     assert(lineCounter(input) === 19);
   });
 });