Bump element-ui from 2.15.1 to 2.15.6 in /template

Bumps [element-ui](https://github.com/ElemeFE/element) from 2.15.1 to 2.15.6.
- [Release notes](https://github.com/ElemeFE/element/releases)
- [Changelog](https://github.com/ElemeFE/element/blob/dev/CHANGELOG.en-US.md)
- [Commits](ElemeFE/element@v2.15.1...v2.15.6)

---
updated-dependencies:
- dependency-name: element-ui
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

template/package.json

@@ -19,7 +19,7 @@
     "eslint-plugin-nuxt": "^3.1.0",
     "eslint-plugin-vue": "^8.1.1",
     "roboto-fontface": "^0.10.0",
-    "element-ui": "2.15.1",
+    "element-ui": "2.15.6",
     "eslint": "8.1.0",
     "eslint-friendly-formatter": "4.0.1",
     "eslint-loader": "4.0.2",