Transfer my (@bitjammer) ownership to Xi Ge (@nkcsgexi)

I hereby transfer ownership of the following libraries to Xi Ge!

- Markup
- Migrator
- lib/Syntax

Author: bitjammer

CODE_OWNERS.TXT

@@ -15,9 +15,9 @@ N: Erik Eckstein
 E: [email protected]
 D: SILOptimizer
 
-N: David Farler
-E: dfarler@apple.com
-D: Markup, lib/Syntax, Swift Linux port
+N: Xi Ge
+E: xi_ge@apple.com
+D: Markup, Migrator, lib/Syntax
 
 N: Doug Gregor
 E: [email protected]