.gitignore: ignore *.tar

Running make tar-pkg results in following:

# Untracked files:
# (use "git add <file>..." to include in what will be committed)
#
# linux-4.0.0-rc3-next-20150313-150225--x86.tar

This patch makes git ignore *.tar files.
Running 'git ls-files -i --exclude-standard' does not show any
tar files excluded from tracking after the change.

Signed-off-by: Andrey Skvortsov <[e-mail]>
Cc: Michal Marek <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Boaz Harrosh <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Benjamin Romer <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

.gitignore

···
 *.order
 *.elf
 *.bin
+*.tar
 *.gz
 *.bz2
 *.lzma