Update globs.md (#4476)

### Problem

`globs.md` was explaining globs using the outdated subtraction-based excludes.

### Solution

Use the `exclude` syntax. Fixes #4473

src/docs/common_tasks/globs.md

@@ -28,7 +28,7 @@ You can also exclude files from a particular directory:
 
     ::python
     scala_library(name='scala',
-      sources=rglobs('*.scala') - rglobs('dir_to_exclude/*.scala')
+      sources=rglobs('*.scala', exclude=[rglobs('dir_to_exclude/*.scala')]),
     )
 
 ## See Also