tools: update eslint config

This makes sure the eslint config is up to date for eslint 6.0.0.

PR-URL: #27670
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Refael Ackermann (רפאל פלחי) <refack@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>

.eslintrc.js

@@ -147,7 +147,7 @@ module.exports = {
     'no-octal': 'error',
     'no-path-concat': 'error',
     'no-proto': 'error',
-    'no-redeclare': 'error',
+    'no-redeclare': ['error', { 'builtinGlobals': false }],
     'no-restricted-modules': ['error', 'sys'],
     /* eslint-disable max-len */
     'no-restricted-properties': [