fix(package): update github-slugger to version 1.2.0

Author: greenkeeper[bot]

package.json

@@ -26,7 +26,7 @@
     "doctrine-temporary-fork": "2.0.0-alpha-allowarrayindex",
     "get-port": "^3.1.0",
     "git-url-parse": "^6.0.1",
-    "github-slugger": "1.1.3",
+    "github-slugger": "1.2.0",
     "glob": "^7.0.0",
     "globals-docs": "^2.3.0",
     "highlight.js": "^9.1.0",