Keep sourceMap as string

Fixes [object Object] being written to source map file.

lib/index.js

@@ -161,8 +161,6 @@ function getOptions(options) {
   };
 
   options.success = function() {
-    options.result.sourceMap = JSON.parse(options.result.sourceMap);
-
     var stats = endStats(options.result.stats);
 
     if (success) {

test/cli.js

@@ -191,16 +191,17 @@ describe('cli', function() {
 
     it('should compile with the --source-map option', function(done) {
       var src = fixture('source-map/index.scss');
-      var dest = fixture('source-map/index.css');
-      var expected = read(fixture('source-map/expected.css'), 'utf8').trim().replace(/\r\n/g, '\n');
-      var map = fixture('source-map/index.map');
-      var bin = spawn(cli, [src, '--output', path.dirname(dest), '--source-map', map]);
+      var destCss = fixture('source-map/index.css');
+      var destMap = fixture('source-map/index.map');
+      var expectedCss = read(fixture('source-map/expected.css'), 'utf8').trim().replace(/\r\n/g, '\n');
+      var expectedMap = read(fixture('source-map/expected.map'), 'utf8').trim().replace(/\r\n/g, '\n');
+      var bin = spawn(cli, [src, '--output', path.dirname(destCss), '--source-map', destMap]);
 
       bin.on('close', function () {
-        assert.equal(read(dest, 'utf8').trim(), expected);
-        assert(fs.existsSync(map));
-        fs.unlinkSync(map);
-        fs.unlinkSync(dest);
+        assert.equal(read(destCss, 'utf8').trim(), expectedCss);
+        assert.equal(read(destMap, 'utf8').trim(), expectedMap);
+        fs.unlinkSync(destMap);
+        fs.unlinkSync(destCss);
         done();
       });
     });

test/fixtures/source-map/expected.map

+{
+	"version": 3,
+	"file": "index.css",
+	"sources": [
+		"index.scss"
+	],
+	"sourcesContent": [],
+	"mappings": "AAAA;EACE,AAAO;EACP,AAAQ;;AAGV,AAAQ;EACN,AAAiB;;AAGnB,AAAQ;EACN,AAAO;EAAT,AAAQ,AAAG;IAGP,AAAa",
+	"names": []
+}