Merge pull request #763 from 0xc0170/fix_maintainers

workflow: update maintainers

Author: Amanda Butler

docs/reference/contributing/guidelines/workflow.md

@@ -20,10 +20,9 @@ The current maintainers are:
 
 - [Anna Bridge](https://os.mbed.com/users/AnnaBridge).
 - [Martin Kojtal](https://os.mbed.com/users/Kojto).
-- [Jimmy Brisson](https://os.mbed.com/users/theotherjimmy).
 - [Shrikant Tudavekar](https://os.mbed.com/users/shrikant1213).
-- [Sam Grove](https://os.mbed.com/users/sam_grove).
-- [Cruz Monrreal](https://os.mbed.com/users/MrCruz).
+- [Nir Sonnenschein](https://os.mbed.com/users/nirs).
+- [Cruz Monrreal](https://os.mbed.com/users/CM2).
 - [Kevin Bracey](https://os.mbed.com/users/kjbracey).
 
 ### Contributions