Fix the 'Hook already exists: pre-push' warnning.

Author: domchen

package.json

@@ -1,6 +1,6 @@
 {
   "name": "depsync",
-  "version": "1.3.14",
+  "version": "1.3.15",
   "author": "Dom Chen",
   "homepage": "https://github.com/domchen/depsync",
   "description": "Automatically synchronize the dependencies of a project by the DEPS configuration file.",

src/tasks/SubRepoTask.js

@@ -47,7 +47,8 @@ SubRepoTask.prototype.run = function (callback) {
     }
     let lfsConfig = path.resolve(repoPath, ".gitattributes");
     if (fs.existsSync(lfsConfig)) {
-        if (!LFSInited) {
+        let prePushFile = path.resolve(repoPath, ".git", "hooks", "pre-push");
+        if (!LFSInited && !fs.existsSync(prePushFile)) {
             Utils.exec("git lfs install", repoPath, true);
             LFSInited = true;
         }