Update dependency element-ui to v2.15.1

Author: renovate-bot

template/package.json

@@ -21,7 +21,7 @@
     "compass-mixins": "0.12.10",
     "cross-env": "7.0.2",
     "echarts": "4.8.0",
-    "element-ui": "2.13.2",
+    "element-ui": "2.15.1",
     "express": "4.17.1",
     "mdi": "2.2.43",
     "nuxt": "2.13.0",