[ImgBot] Optimize images

*Total -- 1,860.89kb -> 919.49kb (50.59%)

/basic_sorting/sorting_insertion.gif -- 1,220.60kb -> 479.02kb (60.76%)
/basic_data_structure/data_structure.png -- 114.44kb -> 70.40kb (38.48%)
/basic_data_structure/array/array.png -- 41.53kb -> 25.66kb (38.22%)
/basic_data_structure/linked_list/linked_list.png -- 53.91kb -> 35.41kb (34.31%)
/basic_data_structure/heap/heap.png -- 51.30kb -> 33.89kb (33.95%)
/basic_data_structure/queue/queue.png -- 37.00kb -> 24.99kb (32.46%)
/basic_data_structure/stack/stack.png -- 37.32kb -> 25.25kb (32.34%)
/basic_data_structure/tree/tree.png -- 68.87kb -> 47.17kb (31.51%)
/basic_data_structure/graph/graph.png -- 89.23kb -> 62.25kb (30.24%)
/basic_data_structure/hash_table/hash_table.png -- 105.46kb -> 75.74kb (28.18%)
/basic_sorting/sorting_selection.gif -- 41.23kb -> 39.72kb (3.66%)

Signed-off-by: ImgBotApp <ImgBotHelp@gmail.com>

Author: ImgBotApp