pin down gulp-header version

Due to gulp-community/gulp-header#21

Author: mohsen1

package.json

@@ -26,7 +26,7 @@
     "gulp-angular-templatecache": "^1.7.0",
     "gulp-concat": "^2.6.0",
     "gulp-connect": "^2.2.0",
-    "gulp-header": "^1.2.2",
+    "gulp-header": "1.2.2",
     "gulp-jscs": "^1.6.0",
     "gulp-jshint": "^1.11.2",
     "gulp-karma": "0.0.4",