Upgrade to ESLint 5

Summary:
Wanted to do that for a while, but the previous eslint error
blocked me. Continues running with the same level or warnings.

Reviewed By: jknoxville

Differential Revision: D13818478

fbshipit-source-id: ac12888dd4177316020c947925d4ff9d64784140

.eslintrc.js

@@ -27,6 +27,6 @@ module.exports = {
 
     // additional rules for this project
     'header/header': [2, 'block', {pattern}],
-    'prettier/prettier': [2, 'fb', '@format'],
+    'prettier/prettier': [2, {requirePragma: true}],
   },
 };