chore: update dependency prettier to v1.9.1

Author: renovate[bot]

package.json

@@ -95,7 +95,7 @@
     "lerna": "2.5.1",
     "lint-staged": "6.0.0",
     "npx": "9.7.1",
-    "prettier": "1.8.2",
+    "prettier": "1.9.1",
     "xo": "0.18.2",
     "yarn": "1.3.2"
   }

yarn.lock

@@ -5542,9 +5542,9 @@ preserve@^0.2.0:
   version "0.2.0"
   resolved "https://registry.npmjs.org/preserve/-/preserve-0.2.0.tgz#815ed1f6ebc65926f865b310c0713bcb3315ce4b"
 
-prettier@1.8.2:
-  version "1.8.2"
-  resolved "https://registry.npmjs.org/prettier/-/prettier-1.8.2.tgz#bff83e7fd573933c607875e5ba3abbdffb96aeb8"
+prettier@1.9.1:
+  version "1.9.1"
+  resolved "https://registry.npmjs.org/prettier/-/prettier-1.9.1.tgz#41638a0d47c1efbd1b7d5a742aaa5548eab86d70"
 
 pretty-format@^18.1.0:
   version "18.1.0"