Modify api for convertCaseCacheSize option

Author: danivek

Diff for: README.md

@@ -65,14 +65,15 @@ Serializer.register(type, options);
 
 To avoid repeating the same options for each type, it's possible to add global options on `JSONAPISerializer` instance:
 
-When using convertCase, a LRU cache is utilized for optimization. The default size of the cache is 5000 per conversion type. The size of the cache can be set by passing in a second parameter to the instance. Passing in 0 will result in a LRU cache of infinite size.
+When using convertCase, a LRU cache is utilized for optimization. The default size of the cache is 5000 per conversion type. The size of the cache can be set with the `convertCaseCacheSize` option. Passing in 0 will result in a LRU cache of infinite size.
 
 ```javascript
 var JSONAPISerializer = require("json-api-serializer");
 var Serializer = new JSONAPISerializer({
   convertCase: "kebab-case",
-  unconvertCase: "camelCase"
-}, 0);
+  unconvertCase: "camelCase",
+  convertCaseCacheSize: 0
+});
 ```
 
 ## Usage

Diff for: lib/JSONAPISerializer.js

@@ -26,13 +26,14 @@ const { validateOptions, validateDynamicTypeOptions, validateError } = require('
  *
  * @class JSONAPISerializer
  * @param {object} [opts] Global options.
- * @param {number} [convertCaseCacheSize=5000] Size of cache used for convertCase, 0 results in an infinitely sized cache
  */
 module.exports = class JSONAPISerializer {
-  constructor(opts, convertCaseCacheSize = 5000) {
+  constructor(opts) {
     this.opts = opts || {};
     this.schemas = {};
 
+    // Size of cache used for convertCase, 0 results in an infinitely sized cache
+    const { convertCaseCacheSize = 5000 } = this.opts;
     // Cache of strings to convert to their converted values per conversion type
     this.convertCaseMap = {
       camelCase: new LRU(convertCaseCacheSize),