Update errors.spec.js (#718)

* Update errors.spec.js

Updating errors.spec.js to use const/let appropriately instead of var.

* Update errors.spec.js

- Changed corrected 'using' to 'use'.
- Changed 'let' to 'const' becuase the're not being changed during the function scope.

tests/spec/errors.spec.js

@@ -1,5 +1,7 @@
-var Filer = require('../../src');
-var expect = require('chai').expect;
+'use strict';
+
+const Filer = require('../../src');
+const expect = require('chai').expect;
 
 describe('Filer.Errors', function() {
   it('has expected errors', function() {
@@ -135,15 +137,15 @@ describe('Filer.Errors', function() {
   });
 
   it('should include all expected properties by default', function() {
-    var err = new Filer.Errors.ENOENT();
+    const err = new Filer.Errors.ENOENT();
     expect(err.name).to.equal('ENOENT');
     expect(err.code).to.equal('ENOENT');
     expect(err.errno).to.equal(34);
     expect(err.message).to.equal('no such file or directory');
   });
 
   it('should include extra properties when provided', function() {
-    var err = new Filer.Errors.ENOENT('This is the message', '/this/is/the/path');
+    const err = new Filer.Errors.ENOENT('This is the message', '/this/is/the/path');
     expect(err.name).to.equal('ENOENT');
     expect(err.code).to.equal('ENOENT');
     expect(err.errno).to.equal(34);
@@ -152,29 +154,29 @@ describe('Filer.Errors', function() {
   });
 
   it('should include default message and path info when provided', function() {
-    var err = new Filer.Errors.ENOENT(null, '/this/is/the/path');
+    const err = new Filer.Errors.ENOENT(null, '/this/is/the/path');
     expect(err.message).to.equal('no such file or directory');
     expect(err.path).to.equal('/this/is/the/path');
   });
 
   it('should include just the message when no path provided', function() {
-    var err = new Filer.Errors.ENOENT();
+    const err = new Filer.Errors.ENOENT();
     expect(err.message).to.equal('no such file or directory');
     expect(err.path).not.to.exist;
   });
 
   it('should not include path in toString() when not provided', function() {
-    var err = new Filer.Errors.ENOENT('This is the message');
+    const err = new Filer.Errors.ENOENT('This is the message');
     expect(err.toString()).to.equal('ENOENT: This is the message');
   });
 
   it('should include path in toString() when provided', function() {
-    var err = new Filer.Errors.ENOENT(null, '/this/is/the/path');
+    const err = new Filer.Errors.ENOENT(null, '/this/is/the/path');
     expect(err.toString()).to.equal('ENOENT: no such file or directory, \'/this/is/the/path\'');
   });
 
   it('should include message and path info when provided', function() {
-    var err = new Filer.Errors.ENOENT('This is the message', '/this/is/the/path');
+    const err = new Filer.Errors.ENOENT('This is the message', '/this/is/the/path');
     expect(err.message).to.equal('This is the message');
     expect(err.path).to.equal('/this/is/the/path');
   });