spelling: nonexistent

Signed-off-by: Josh Soref <[email protected]>

Author: jsoref

test/attr/private_import.swift

@@ -4,6 +4,6 @@
 
 @_private(sourceFile: "Array.swift") import Swift // expected-error {{module 'Swift' was not compiled for private import}}
 @_private(sourceFile: "empty.swift") import empty // no-error
-@_private(sourceFile: "not_existing_file.swift") import empty // no-error
+@_private(sourceFile: "nonexistent_file.swift") import empty // no-error
 
 @_private(sourceFile: "none") func foo() {} // expected-error {{@_private may only be used on 'import' declarations}} {{1-31=}}