.gitignore: ignore run.gdb

* .gitignore: ignore run.gdb which is assumed to be generated
  by make gdb and customized manually during development

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59680 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

.gitignore

@@ -113,6 +113,7 @@ lcov*.info
 /ruby-runner
 /ruby-runner.h
 /ruby-man.rd.gz
+/run.gdb
 /sizes.c
 /test.rb
 /tmp