fix: disable stash by default when using diff option (#1259)

Author: yuzhanglong

lib/index.js

@@ -75,7 +75,8 @@ const lintStaged = async (
     quiet = false,
     relative = false,
     shell = false,
-    stash = true,
+    // Stashing should be disabled by default when the `diff` option is used
+    stash = diff === undefined,
     verbose = false,
   } = {},
   logger = console