[crashlog] Strip trailing `\n` from check_output return.

Generally having spurious `\n` doesn't matter, but here the
returning string is a command which is executed, so  we want
to strip it. Pointed out by Jason.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@358717 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed