Use a .prettierrc to allow editors to pick up Prettier config.

This allows editors to pick up the Prettier config. Combined with a "format on save" option, this cleans up the output of `git diff` prior to committing since files get formatted with Prettier when a user saves a file.

Author: Mike Nikles

.prettierignore

@@ -1 +1,2 @@
 flow-typed
+package.json

.prettierrc

@@ -0,0 +1,4 @@
+{
+  "singleQuote": true,
+  "trailingComma": "es5"
+}

package.json

@@ -257,7 +257,7 @@
   },
   "lint-staged": {
     "*.js": [
-      "prettier --write --single-quote --trailing-comma es5",
+      "prettier --write",
       "eslint --fix",
       "git add"
     ]