update addons.md to consider the build type

When running:
$ rm test/addons/.docbuildstamp
$ make test/addons/.docbuildstamp

A numder of JavaScript test files are generated. These have hard codes
paths to build/Release/addons. This commit updates these paths to
consider the type of build being performed.

Author: danbev

doc/api/addons.md

@@ -138,7 +138,8 @@ Once built, the binary Addon can be used from within Node.js by pointing
 
 ```js
 // hello.js
-const addon = require('./build/Release/addon');
+const buildType = process.config.target_defaults.default_configuration;
+const addon = require(`./build/${buildType}/addon`);
 
 console.log(addon.hello()); // 'world'
 ```
@@ -316,7 +317,8 @@ Once compiled, the example Addon can be required and used from within Node.js:
 
 ```js
 // test.js
-const addon = require('./build/Release/addon');
+const buildType = process.config.target_defaults.default_configuration;
+const addon = require(`./build/${buildType}/addon`);
 
 console.log('This should be eight:', addon.add(3, 5));
 ```
@@ -369,7 +371,8 @@ To test it, run the following JavaScript:
 
 ```js
 // test.js
-const addon = require('./build/Release/addon');
+const buildType = process.config.target_defaults.default_configuration;
+const addon = require(`./build/${buildType}/addon`);
 
 addon((msg) => {
   console.log(msg); // 'hello world'
@@ -419,7 +422,8 @@ To test it in JavaScript:
 
 ```js
 // test.js
-const addon = require('./build/Release/addon');
+const buildType = process.config.target_defaults.default_configuration;
+const addon = require(`./build/${buildType}/addon`);
 
 var obj1 = addon('hello');
 var obj2 = addon('world');
@@ -477,7 +481,8 @@ To test:
 
 ```js
 // test.js
-const addon = require('./build/Release/addon');
+const buildType = process.config.target_defaults.default_configuration;
+const addon = require(`./build/${buildType}/addon`);
 
 var fn = addon();
 console.log(fn()); // 'hello world'
@@ -639,7 +644,8 @@ Test it with:
 
 ```js
 // test.js
-const addon = require('./build/Release/addon');
+const buildType = process.config.target_defaults.default_configuration;
+const addon = require(`./build/${buildType}/addon`);
 
 var obj = new addon.MyObject(10);
 console.log(obj.plusOne()); // 11
@@ -831,7 +837,8 @@ Test it with:
 
 ```js
 // test.js
-const createObject = require('./build/Release/addon');
+const buildType = process.config.target_defaults.default_configuration;
+const createObject = require(`./build/${buildType}/addon`);
 
 var obj = createObject(10);
 console.log(obj.plusOne()); // 11
@@ -1007,7 +1014,8 @@ Test it with:
 
 ```js
 // test.js
-const addon = require('./build/Release/addon');
+const buildType = process.config.target_defaults.default_configuration;
+const addon = require(`./build/${buildType}/addon`);
 
 var obj1 = addon.createObject(10);
 var obj2 = addon.createObject(20);
@@ -1091,7 +1099,8 @@ Test in JavaScript by running:
 
 ```js
 // test.js
-const addon = require('./build/Release/addon');
+const buildType = process.config.target_defaults.default_configuration;
+const addon = require(`./build/${buildType}/addon`);
 ```
 
 [bindings]: https://github.com/TooTallNate/node-bindings