.eslintrc.js: Use trailingComma: "es5" with Prettier

This addresses prettier#3469
as outlined in prettier#3469 (comment)

The corresponding formatting changes will be done separately for
clarity's sake.

.eslintrc.js

@@ -3,15 +3,15 @@
 module.exports = {
   env: {
     es6: true,
-    node: true
+    node: true,
   },
   extends: ["eslint:recommended", "plugin:react/recommended"],
   plugins: ["prettier", "react", "import"],
   rules: {
     curly: "error",
     "import/no-extraneous-dependencies": [
       "error",
-      { devDependencies: ["tests*/**", "scripts/**"] }
+      { devDependencies: ["tests*/**", "scripts/**"] },
     ],
     "no-console": "off",
     "no-else-return": "error",
@@ -22,15 +22,15 @@ module.exports = {
     "one-var": ["error", "never"],
     "prefer-arrow-callback": "error",
     "prefer-const": "error",
-    "prettier/prettier": "error",
+    "prettier/prettier": ["error", { trailingComma: "es5" }],
     "react/no-deprecated": "off",
     strict: "error",
     "symbol-description": "error",
-    yoda: ["error", "never", { exceptRange: true }]
+    yoda: ["error", "never", { exceptRange: true }],
   },
   parserOptions: {
     ecmaFeatures: {
-      jsx: true
-    }
-  }
+      jsx: true,
+    },
+  },
 };