Only run ALE linter after save

Author: keith

ale_linters/swift/swiftpm.vim

@@ -65,4 +65,5 @@ call ale#linter#Define('swift', {
       \ 'executable_callback': 'ale_linters#swift#swiftpm#GetExecutable',
       \ 'command_callback': 'ale_linters#swift#swiftpm#GetCommand',
       \ 'callback': 'ale_linters#swift#swiftpm#Handle',
+      \ 'lint_file': 1,
     \ })