Prefer += and -=
Prefer += and -=

Change-Id: I0b1ba2e7c8287340eebec7eb9b3e1aea8945d82f

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core