chore(package): update gulp-bump to version 3.1.3

Closes #62

Author: greenkeeper[bot]

package.json

@@ -65,7 +65,7 @@
     "cssnano": "^4.1.7",
     "del": "3.0.0",
     "gulp": "3.9.1",
-    "gulp-bump": "3.1.1",
+    "gulp-bump": "3.1.3",
     "gulp-conventional-changelog": "^2.0.3",
     "gulp-coveralls": "0.1.4",
     "gulp-file": "0.4.0",