Update CHANGELOG.md

Author: Olga Danylova

CHANGELOG.md

@@ -1,5 +1,8 @@
 # RELEASE HISTORY
 
+## 5.0.6 July 2, 2018
+* JSONHelper class fixed to proceed NSNull values correctly
+
 ## 5.0.5 June 28, 2018
 * MessagingService class is now ARC-based
 * Async unregisterDevice method fixed
@@ -12,11 +15,11 @@
 * Socket.IO updated to v13.2.1
 
 ## 5.0.1 June 7, 2018
-* pod 'Backendless' command is used for all platforms.
+* pod 'Backendless' command is used for all platforms
 
 ## 5.0 June 6, 2018
 * RT support added
-* API changes. Please check the documentation.
+* API changes. Please check the documentation
 
 ## 4.5.0 April 4, 2018
 * Bulk create method now returns array of objectIds