gitignore: never ignore debug module

On case-insensitive platorms, the Debug/ rule catches the debug module
under npm and eslint.

PR-URL: https://github.com/nodejs/node/pull/2286
Reviewed-By: Roman Reiss <me@silverwind.io>

.gitignore

@@ -24,7 +24,7 @@ icu_config.gypi
 
 # various stuff that VC++ produces/uses
 Debug/
-!deps/npm/node_modules/node-gyp/node_modules/path-array/node_modules/array-index/node_modules/debug
+!**/node_modules/debug/
 !deps/v8/src/debug/
 Release/
 !doc/blog/**