Use tmp directory for files written during tests

- Add spec/tmp directory with .gitkeep file to indicate the folder is intentional
- Add the folder contents to .gitignore
- Use this folder to output the sourcemap file during bin tests. This file is a sideeffect of the main test

Author: ErisDS

.gitignore

@@ -17,3 +17,4 @@ lib/handlebars/compiler/parser.js
 /coverage/
 /dist/
 /integration-testing/*/dist/
+/spec/tmp/*

spec/artifacts/source.map.amd.txt

@@ -0,0 +1 @@
+This directory is ignored in .gitignore. It can be used to write temporary files during tests.

spec/expected/source.map.amd.js

@@ -155,7 +155,7 @@ const testCases = [
       '-N',
       'test',
       '--map',
-      './spec/artifacts/source.map.amd.txt'
+      './spec/tmp/source.map.amd.txt'
     ],
     outputLocation: 'stdout',
     expectedOutputSpec: './spec/expected/source.map.amd.js'