gitk: Fix copyright symbol in About box message
gitk: Fix copyright symbol in About box message

Somehow it got corrupted in commit d93f1713 ("gitk: Use themed tk
widgets").

Signed-off-by: Paul Mackerras <19a0ba370c443ba08d20b5061586430ab449ee8c@samba.org>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git