Remove wit.ai parts and update readme

Author: Christoph Rumpel

.env.example

@@ -2,6 +2,5 @@
 WEBHOOK_VERIFY_TOKEN=
 PAGE_ACCESS_TOKEN=
 
-# Bot platforms
+# NLP platform
 DIALOGFLOW_TOKEN=
-WITAI_TOKEN=

composer.json

@@ -3,8 +3,7 @@
         "iboldurev/dialogflow": "^0.3.0",
         "monolog/monolog": "^1.23",
         "vlucas/phpdotenv": "^2.4",
-        "phpunit/phpunit": "^5.5",
-        "tgallice/wit-php": "^0.3.1"
+        "phpunit/phpunit": "^5.5"
     },
     "autoload": {
         "psr-4": {