Rewrite local git detection using git command

lib/detectLocalGit.js

@@ -1,9 +1,7 @@
+var execSync = require('child_process').execSync;
 var fs = require('fs');
 var path = require('path');
 
-// branch naming only has a few excluded characters, see git-check-ref-format(1)
-var REGEX_BRANCH = /^ref: refs\/heads\/([^?*\[\\~^:]+)$/;
-
 module.exports = function detectLocalGit() {
   var dir = process.cwd(), gitDir;
   while (path.resolve('/') !== dir) {
@@ -18,11 +16,10 @@ module.exports = function detectLocalGit() {
   if (path.resolve('/') === dir)
     return;
 
-  var head = fs.readFileSync(path.join(dir, '.git', 'HEAD'), 'utf-8').trim();
-  var branch = (head.match(REGEX_BRANCH) || [])[1];
+  var commit = execSync('git rev-parse HEAD', {cwd: dir, encoding: 'utf8'}).trim();
+  var branch = execSync('git rev-parse --abbrev-ref HEAD', {cwd: dir, encoding: 'utf8'}).trim();
   if (!branch)
-    return { git_commit: head };
+    return { git_commit: commit };
 
-  var commit = fs.readFileSync(path.join(dir, '.git', 'refs', 'heads', branch), 'utf-8').trim();
   return { git_commit: commit, git_branch: branch };
 };