Update legacy default authentication endpoint

Author: stansypht

OAuthHelper.cs

@@ -10,7 +10,7 @@ namespace Sypht
 {
     class OAuthHelper
     {
-        private const string SYPHT_AUTH_ENDPOINT = "https://auth.sypht.com/oauth2/token";
+        private const string SYPHT_AUTH_ENDPOINT = "https://login.sypht.com/oauth/token";
 
         private String clientId = null;
         private String clientSecret = null;

README.md

@@ -20,9 +20,9 @@ Populate system environment variable with the credentials generated above:
 export SYPHT_API_KEY="<client_id>:<client_secret>"
 ```
 
-If credentials were issued before 16th June 2020, please populate one more system environment variable:
+If credentials were issued after 16th June 2020, please use one more system environment variable:
 ```Bash
-export SYPHT_AUTH_ENDPOINT="https://login.sypht.com/oauth/token"
+export SYPHT_AUTH_ENDPOINT="https://auth.sypht.com/oauth2/token"
 ```
 
 install the json.net dependency