gitk: Add French translation

Signed-off-by: Emmanuel Trillaud <[email protected]>
Signed-off-by: Thomas Moulard <[email protected]>
Signed-off-by: Guy Brand <[email protected]>
Signed-off-by: Nicolas Sebrecht <[email protected]>
Signed-off-by: Paul Mackerras <[email protected]>

Author: Emmanuel Trillaud