Updated changelog

Author: audigex

docs/changelog.txt

@@ -51,6 +51,8 @@ SAVEGAME BREAKING VERSION
 - Added Hull Trains (grey stripe) livery variant for Class 802
 - Amended Class 99 power, service speed, weight, TE for real world values
 - Improved WMR liveries for 196, 730
+- Fixed Class 150 BR blue diagonals having green instead of white
+- Fixed Mk4 coaches being available at any time
 - Fixed dual-voltage trains only appearing on 3rd Rail on some track sets
 - Fixed running cost parameter only applying to one subclass of Class 175
 - Fixed a bunch of sound and power bugs for multimode units