Ignore node_modules when printing warnings (#20363)

This now finds acorn and fails to extract warnings from it. But also, this
seems slow.

Author: sebmarkbage

scripts/print-warnings/print-warnings.js

@@ -90,6 +90,7 @@ gs([
   '!packages/react-devtools*/**/*.js',
   '!**/__tests__/**/*.js',
   '!**/__mocks__/**/*.js',
+  '!**/node_modules/**/*.js',
 ]).pipe(
   through.obj(transform, cb => {
     process.stdout.write(