Update .gitignore

- exclude buck plugin binary
- exclude watchman config

Change-Id: I2f2251f1833466b6dd66f8a23bcc115558330c31

@@ -16,6 +16,8 @@ dependency-reduced-pom.xml
 buck-out
 .buckconfig.local
 .buckjavaargs*
+bucklets/plugins/
+.watchmanconfig
 
 /bin/