core: add lodash deps

Author: kefranabg

Diff for: packages/@vuepress/theme-default/package.json

@@ -34,6 +34,7 @@
     "@vuepress/plugin-nprogress": "^1.0.3",
     "@vuepress/plugin-search": "^1.0.3",
     "docsearch.js": "^2.5.2",
+    "lodash": "^4.17.15",
     "stylus": "^0.54.5",
     "stylus-loader": "^3.0.2",
     "vuepress-plugin-container": "^2.0.0"

Diff for: yarn.lock

@@ -7316,7 +7316,7 @@ lodash.uniq@^4.5.0:
   version "4.5.0"
   resolved "https://registry.yarnpkg.com/lodash.uniq/-/lodash.uniq-4.5.0.tgz#d0225373aeb652adc1bc82e4945339a842754773"
 
-lodash@^4.0.0, lodash@^4.11.2, lodash@^4.17.12:
+lodash@^4.0.0, lodash@^4.11.2, lodash@^4.17.12, lodash@^4.17.15:
   version "4.17.15"
   resolved "https://registry.yarnpkg.com/lodash/-/lodash-4.17.15.tgz#b447f6670a0455bbfeedd11392eff330ea097548"