chore(deps-dev): bump @vuepress/plugin-back-to-top from 1.5.4 to 1.6.0

Bumps [@vuepress/plugin-back-to-top](https://github.com/vuejs/vuepress/tree/HEAD/packages/@vuepress/plugin-back-to-top) from 1.5.4 to 1.6.0.
- [Release notes](https://github.com/vuejs/vuepress/releases)
- [Changelog](https://github.com/vuejs/vuepress/blob/master/CHANGELOG.md)
- [Commits](https://github.com/vuejs/vuepress/commits/v1.6.0/packages/@vuepress/plugin-back-to-top)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -39,7 +39,7 @@
     "devDependencies": {
         "@babel/core": "^7.6.0",
         "@babel/preset-env": "^7.4.5",
-        "@vuepress/plugin-back-to-top": "1.5.4",
+        "@vuepress/plugin-back-to-top": "1.6.0",
         "@vuepress/plugin-google-analytics": "1.6.0",
         "@vuepress/plugin-pwa": "1.6.0",
         "art-template": "4.13.2",

yarn.lock

@@ -1228,10 +1228,10 @@
   dependencies:
     lodash.debounce "^4.0.8"
 
-"@vuepress/plugin-back-to-top@1.5.4":
-  version "1.5.4"
-  resolved "https://registry.yarnpkg.com/@vuepress/plugin-back-to-top/-/plugin-back-to-top-1.5.4.tgz#f7904e1220fcd1cb457a819a6bf963b55c584bea"
-  integrity sha512-FqT3F8VztSiDXtI7xjD4SOeEuyaPYx2zxxU3cH3wfe/amlFWyFPjTWJwAf1GRT5CqS13J2qfEnfWMU/Ct7Xg/Q==
+"@vuepress/plugin-back-to-top@1.6.0":
+  version "1.6.0"
+  resolved "https://registry.yarnpkg.com/@vuepress/plugin-back-to-top/-/plugin-back-to-top-1.6.0.tgz#a10df98b7a4f57c627f72289cd0ab2ff0f075a1d"
+  integrity sha512-nJr/qlBcCN8vUyAb3nZPKqBS1DjfgZJquroOOd41CcLgsq3yAxmWLmxbLjg1MoBxk1Q8TrWz8qI7JRIw7W4aVw==
   dependencies:
     lodash.debounce "^4.0.8"
 
@@ -1275,21 +1275,6 @@
   resolved "https://registry.yarnpkg.com/@vuepress/plugin-search/-/plugin-search-1.6.0.tgz#a064f638a8f30485859b871047deaf9194ffc886"
   integrity sha512-Js7zRmM6/b6dYfnJsSP2MQN0lzjUfSX8l3z9y/QHxK8BaXIx7LdTcQY6FGK4pxuwlWcg02CIUS5BMc1gZKn6Nw==
 
-"@vuepress/shared-utils@1.5.4":
-  version "1.5.4"
-  resolved "https://registry.yarnpkg.com/@vuepress/shared-utils/-/shared-utils-1.5.4.tgz#d2c8693b8cd354d3a13a76f8f4259335e5540099"
-  integrity sha512-HCeMPEAPjFN1Ongii0BUCI1iB4gBBiQ4PUgh7F4IGG8yBg4tMqWO4NHqCuDCuGEvK7lgHy8veto0SsSvdSKp3g==
-  dependencies:
-    chalk "^2.3.2"
-    escape-html "^1.0.3"
-    fs-extra "^7.0.1"
-    globby "^9.2.0"
-    gray-matter "^4.0.1"
-    hash-sum "^1.0.2"
-    semver "^6.0.0"
-    toml "^3.0.0"
-    upath "^1.1.0"
-
 "@vuepress/shared-utils@1.6.0":
   version "1.6.0"
   resolved "https://registry.yarnpkg.com/@vuepress/shared-utils/-/shared-utils-1.6.0.tgz#8bf0c9c4e502bc6f10e70db3b236e816d8165631"