Fix issue 129: not working in windows

lib/tags.js

@@ -1,8 +1,24 @@
 // Packages
 const semVer = require('semver');
 const taggedVersions = require('tagged-versions');
-
-const defaultRev = 'HEAD --first-parent `git rev-parse --abbrev-ref HEAD`';
+const childProcess = require('child-process-promise');
+
+let defaultRev = 'HEAD --first-parent ';
+
+runCommand('git rev-parse --abbrev-ref HEAD').then((output) => {
+	defaultRev += output;
+})
+
+/**
+ * Run shell command and resolve with stdout content
+ *
+ * @param  {string} command Shell command
+ * @return {Promise<string,Error>}
+ */
+function runCommand(command) {
+	return childProcess.exec(command)
+		.then(result => result.stdout);
+}
 
 const defaultOptions = {
 	rev: defaultRev,

package.json

@@ -53,7 +53,8 @@
     "semver": "5.5.0",
     "tagged-versions": "1.3.0",
     "then-sleep": "1.0.1",
-    "update-check": "1.3.2"
+    "update-check": "1.3.2",
+    "child-process-promise": "^2.1.3"
   },
   "eslintConfig": {
     "extends": [