tools: update dotfile whitelist in .gitignore

.eslintrc was renamed in nodejs#7699 to .eslintrc.yaml.

PR-URL: nodejs/node#12116
Refs: nodejs/node#7699
Reviewed-By: Claudio Rodriguez <cjrodr@yahoo.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

.gitignore

@@ -6,7 +6,7 @@
 !tools/doc/node_modules/**/.*
 !.editorconfig
 !.eslintignore
-!.eslintrc
+!.eslintrc.yaml
 !.gitattributes
 !.github
 !.gitignore